A lot of drinking does happen in most residential colleges. However, non-drinkers at most such colleges can find plenty of social activities that do not involve drinking.
It looks like your parents expect you to be like many college students and start drinking in college (despite saying that you will not), so they want you to know the effects of one, two, etc. drinks on yourself under their supervision, so that you will not have to find out the effects at a party or other potentially risky situation. Even if you intend to abstain from drinking, you may want to consider whether finding out the effects of one, two, etc. drinks under parental supervision may be something useful to know before you go to college.