Conversation so far:
Why is the drinking age in the US 21 and not 18?
In short, we ended up with a national minimum age of 21 because of the National Minimum Drinking Age Act of 1984. This law basically told states that they had to enact a minimum drinking age of 21 or lose up to 10 percent of their federal highway funding.

Question: What were the pros and cons
Self-contained rewrite: What were the pros and cons of the the drinking age in the US 21 being and not 18?