I think it comes down to the enviroment you are in. While you are in school socializing is absolutely necessary to help build your professional network. I am in buisness school and I have heard my peers having meetings with professors and company executives in bars. It helps eliminate some of the tension in the meeting. If in your group having a drink with lunch is normal then by all means partake. It shows that you care about the others by following the standard that the group has set.
Once you have finished school and in a corporate environment it comes down to the policies and norms of your organization. Obviously coming to work noticeably intoxicated will land you in trouble anywhere but some organizations are okay with a social drink at lunch. I have visited offices of respected organizations where alcohol was available in the break room
Finally when meeting a client you have to be aware of their company policy on alchol as they may not be able to partake. It's best to err on the side of safety when you do not know as you don't want to be the only one with a drink and appear like an alcholic or make your client feel pressured to drink when they aren't allowed.