Mixed views on this - 20 odd years ago having a beer inside home park would have been unthinkable - I don't think that has lead to anymore issues, so people are already drinking in the stadium and there is no evidence of it leading to an increase in anti-social behaviour that I am aware of.
The big issue would be this culture of lobbing pints around. Stopped going to gigs and festivals about 10 years ago because of this (that and it most likely wasn't lager landing on you) so wouldn't want to be getting soaked inside a stadium with other people's beer. We've seen at the Euro's (Denmark springs to mind) the craze of lobbing beer about when a goal goes in, recently Hungary fans where chucking pint cups onto the pitch in the qualifier so its not just an English craze, but its something we will see if beer in stands becomes a thing.
The big issue would be this culture of lobbing pints around. Stopped going to gigs and festivals about 10 years ago because of this (that and it most likely wasn't lager landing on you) so wouldn't want to be getting soaked inside a stadium with other people's beer. We've seen at the Euro's (Denmark springs to mind) the craze of lobbing beer about when a goal goes in, recently Hungary fans where chucking pint cups onto the pitch in the qualifier so its not just an English craze, but its something we will see if beer in stands becomes a thing.