If an 18 year old can smoke and vote, they should be able to drink. This would help them socialize when used moderately. It would also help to lower crime because 18 year old teenagers are going to drink whether it is legal or not. If it is legal there wouldn't be so many people breaking the law, hence less crime.
Lowering the drinking age to 18 would not at all help 18 year olds socialize better. At that age they are not mature enough to know what to do in that type of situation and the 3 years of waiting is just enough time to let them learn more about themselves and increase their maturity. At 18 its already easy to socialize with people so there is no reason to throw alcohol into the situation. As for it helping lower crime, that is just foolish and if anything it will probably increase the crime rate because a combination of their lack of maturity and them drinking alcohol would make things worse.