For regular punters it wouldn't do any harm at all. Our track record in Scotland, however, shows that there is a sufficiently large minority of roasters that make drinking at the match unworkable. The rules that are in place now came about after years of neddish behaviour on the terraces, a lot of which was due to the booze.
I'm not against alcohol at games in general - I used to enjoy a half time pint when I lived down south and frequented Portman Road. I'd like to think we have moved on since the days of beer cans full of pish flying overhead and vomit on the steps, but I'm not convinced.