Correct, it's mainly to avoid intoxication and the ramifications that come out of it. However, I agree with what those students did. They have principles and they stuck to them. The alcohol could have mixed with the food for instance, even though it wasn't meant to be consumed directly. Secondly, someone could unknowingly consume it thinking it was edible.

As to your first point, highly processed foods are definitely something to watch out for. However, the effects of alcohol are immediate, and can be seen in a single sitting. Countless instances of rape, drunk driving, and homicides that come out of it. You won't see someone consume a couple of meals at a fast food place then lose his decision making ability for instance.