I had a conversation about this with a football supporting friend at work recently. I posed the theortical question about him inviting me to accompany him to a game as friend but a supporter of the opposition team where he is a season ticket holder (Southampton). He told me in all seriousness that I would be discouraged from showing any support for my team if sat in the home section, and if I did dare cheer for my team I would face being ejected by the stewards!
He saw nothing wrong in this and thought it perfectly reasonable. This from an intelligent bloke in his sixties, not some young scally.
Its crazy me and a few mates do home and away fixtures between our respective teams always sitting in the home end and never mind showing support, talling with a northern accent in the Charlton end at The Valley and having far to much in-depth knowledge of "the visitors" raises eye brows - in my experience its most advisable to stay quiet and sit on your hands!
Its a position re-enfornced by clubs, nobody in the game seems to understand that mature adults are capable of mingling and watching sport, supporting opposite sides and not be at each others throats!
Recently sat in the South Stand at Wigan and a team of touring kids, aged about 10 or 12 were cheering on Spurs, raised a few eyebrows, but thankfully everyone was grown up about it and stewards (no doubt used to the rugby!) were sensible and they were allowed to carry on, led to some funny and good hearted banter between the kids.
Another reason to spend time watching non-league football, crowds mingle freely lower down the pryamid and people go home in one piece!