Well of course. But if I have 20 pounds in my pocket and I'm standing outside St Mirren Park on a match day. It's better for the club if I pay to get in than it is if I walk away, agreed?
It's also better for the club if I spend money whilst there. IE buy programmes, merchandise, food etc. If alcohol was introduced the average spend per punter would go up in the stadium, I don't think there's any doubt about that. The club would make a profit on the alcohol sales and the extra profit would be sufficient to subside ticket prices if the club chose to do so IMO.
We will never know though, because it will never happen.