I find myself largely neutral on gun control. I don't have a gun myself, nor can I currently imagine ever being in a position of owning one. I could probably count on one hand the times I've fired a gun, all in Boy Scouts, and all years and years ago. It just doesn't affect me. I have a lot of hunting friends and families, and have known people even here in the United States who really did depend on hunting for their food -- one of my friends in high school in South Dakota had to go hunting every year, despite the fact that she hated it, because they needed that extra little bit to take the pressure off. So I have no sympathy at all with the No Guns Ever crowd. But beyond that, I don't really have much of an opinion about the particular legal regulations used to keep order in this area of human life.
But I do have a pedantic streak in me, and even I, who have not touched a gun in something like twenty years, know what a semiautomatic is, and it gets annoying to keep coming across people who clearly don't yet insist on saying something about it. Semiautomatic does not mean 'scarier'. A semiautomatic rifle, for instance, is neither the most powerful, nor the most accurate, nor the most reliable rifle. There is one and only one thing that makes a gun semiautomatic:
It reloads automatically, but does not fire more than one bullet per trigger-squeeze.
While it varies considerably, for engineering reasons, semiautomatic weapons tend to be less powerful, less accurate, and less reliable (more likely to fail) than manual action weapons, in which the gun is reloaded by pulling or sliding something. Since they are self-loading and thus cut out loading time, semiautomatic weapons have a certain amount of convenience to them, which is why they are popular. But military snipers, for instance, almost universally use bolt-action rifles, with manual reloading: bolt-action rifles are usually better than semiautomatic rifles in power, accuracy, and reliability, and snipers can easily afford the tiny amount of extra loading time if it gives them an extra advantage in those three areas.
What is more, even though a semiautomatic weapon saves on loading time, this is really a very small amount of time. A pro with his favorite pump-action rifle is not going to be at any serious disadvantage in speed compared to most people with a semiautomatic. So, in other words, 'semiautomatic' is purely a term for how the gun is loaded (how the bullet is chambered); it tells us nothing else whatsoever.
It is, on the other hand, useful, as opposed to 'assault', which is a bizarre mish-mash category. MrD had some recent interesting posts about this category:
Assault Weapons Part 1: Battle Rifle to Assault Rifle
Assault Weapons Part 2: Assault Rifles vs. "Assault Weapons"
Assault Weapons Part 3: Gun Control