Most of his arguments are irrelevant to the point at hand; merely establishing that something is ethically important doesn't give you much information about the appropriate practical action with respect to it. If he actually knew anything about serious Catholic ethics, he would know as well that "for the greater good" is not itself usually accepted in Catholic ethics as a ground of practical action or policy; Catholic moral theology is intrinsically non-consequentialist, so "for the greater good" is generally only accepted when the relevant action or policy can be established as morally good on independent grounds, which is precisely at issue here. It's also a standard view in Catholic moral theology that you can't have conflicting moral obligations except where one's conscience is either badly formed or misinformed, and even if you had a more generous view, to decide such conflicts on the basis of "the greater good" would be ethically suspect at best.
The primary problem even with his ethical arguments, though, is that Bird (like most non-Catholics) confuses the Seal with ministerial privilege. Ministerial privilege is for the protection of the penitent; it is exactly like the sort of privilege between doctors and patients or between lawyers and clients, and like those it is something that should not be easily broken, but is not unbreakable, and reporting requirements in matters of crimes are usually consistent with the privilege. If a priest, outside the confessional, discovers that a crime has been committed, he has a professional responsibility to do something about it. But the confessional is a distinct form of confidence, one in which the priest's primary obligation is to God, and in Catholic sacramental theology, the Seal of the Confessional is recognized a responsibility arising from the priest's acting on behalf of God; it is an obligation with divine backing, intrinsic to the sacrament's character as the divine "tribunal of mercy". Confession in a context where there is no guarantee of the Seal is not sacramental confession; it can be a good thing, but the constitution of the confessional as a divine tribunal makes it an entirely different matter than just spiritual direction or the priest's role as an advisor. Thus the ethical arguments that Bird actually considers only really bear on the ministerial privilege; but this is an otiose argument, since crime reporting requirements are already part of any usual conception of a priest's ministerial privilege. For the Seal, you would need a completely different kind of argument to begin with, one that took into account the divine character of the confessional.
It's worth noting, incidentally, that although Bird only focuses on priests, the Seal of Confession applies generally -- because it's intrinsic to the sacrament, no Catholic can legitimately break it. If you are a layperson, and you happen to overhear part of someone's sacramental confession and tell someone else what you heard, you have committed a grave sin and profaned a holy thing. No one is exempted.
But, of course, what makes his argument an absolute non-starter for Catholics is that it is based on an Anglican, and not a Catholic, theology of the sacraments. Bird doesn't actually engage with any Catholic sacramental theology anywhere in his discussion, and says:
Third, Catholic faith requires both organic development of its doctrine and resourcement of its ancient tradition to effectively address the problem of abusive priests. The origins of penance and the seal of the confession are developments from the medieval and counter-reformation periods. Just as the seal of the confessional was a necessary development to ensure the confidentiality of the confessional and to prevent the exploitation of the contrite, so too is it now necessary to develop a theology and practice to protect the victims of the penitent in the case of sexual violence. What this requires is not a renouncement of the seal of the confessional, but its refinement to suit the pastoral needs of a congregation.
This is part of what I mean by the passive-aggressively anti-Catholic character of the essay. Putting out theological cover by the jargonistic misuse of the terms "organic development of...doctrine" and "ressourcement of...ancient tradition" (none of which are given any definite content here), he immediately appeals to anti-Catholic stereotypes by making it about abusive priests rather than every sort of abuser, and goes on in the next sentence to make a claim that is equivalent to saying that Catholic sacramental theology of penance is false and needs to be replaced. He then incoherently says that making the Seal not be a seal is not a renouncement of the Seal, but a refinement (a term that is also not given any content here, because he does not start with Catholic theology and ask how it could be refined). His proposal would not be an "organic development" by any standard theological use of the term, but a rupture, a complete repudiation of the Tridentine notion of sacramental reconciliation as a divine tribunal of mercy, based not on any genuine Catholic ressourcement but on his assumption that Catholics are just making up the idea that there has to be a Seal of Confession, based on what looks rather like kind of general practical stupidity, it having apparently never occurred to any Catholic in the entire history of the doctrine that the Seal might sometimes make the responsibility of protecting people complicated. (In fact, of course, there is a long history of discussion about the best ways to handle these matters, all of which Bird ignores.)
We get more of the passive-agressive anti-Catholicism as we go further; talking about two cases in which he was mistreated because under the circumstances people were probably mistaking him for a Catholic priest, he says:
I do not think the two assailants hate Catholics because of decisions made at the Fourth Lateran Council, nor because of the doctrine of transubstantiation, nor because of strong feelings about Notre Dame University or Celtic F.C. in Glasgow. It is a hatred based on child sexual abuse, its cover-up, its perpetuation, and failing to do what must be done to deal with it. It is a hatred that is, I believe, entirely understandable.
Hating random people for things other people did is not "understandable"; it is irrational and immoral, and reasonable people actively avoid doing it. We aren't, remember, talking about someone hating someone they know has abused a child or covered up for an abuser, nor even about someone hating another on the basis of an allegation. We're talking about someone picking out a stranger on the street and abusing him because he looked like he might be Catholic. It is as completely unacceptable as people assaulting Sikhs because a handful of Muslims flew planes into buildings; it would be as wrong were they assaulting Muslims, but the nature of the actual wrong shows in blazing light the sheer moral stupidity and bigotry of the action in the first place. And what is Bird's solution to this problem of Australian anti-Catholic bigotry that leads to people harassing strangers for being Catholic? The Catholics need to change so they are no longer giving other people excuses for being bigots.
To be honest, I would have much greater respect for Bird's argument if he actually said what he is in fact insisting, that the state has the right to outlaw what Catholics think of as the sacrament of confession, and Catholics should just put up with it and fall back on an entirely different, and wholly non-sacramental form of confession, one more like moral therapy than like absolution before the judgment seat of God. And, of course, it's not as if Catholics have not been in similar situations before, although usually people have gone after Mass rather than confession. It's not as if it's not obvious what is really going on, because people do things like this only as part of a large packet of things motivated by anti-Catholic sentiments. It doesn't really make difference one way or another; it just would be easier if non-friends like Bird would stop pretending to be friends on the topic, and also admit openly what they are actually demanding of Catholics rather than trying to pretty it up with theological jargon that in context has no real meaning. The Catholic sacraments are what they are; if you can't tolerate them, or if you think other people shouldn't have to tolerate them, just say so. Everyone will be better off for it.