I agree, but that then puts too much literalness on the word 'supporter'.

In my opinion, calling yourself a fan, supporter, follower or anything of the like is the same thing. If you don't go to games and someone asks you who you support, you aren't going to say "well I don't support anyone as I don't go to games, but I'm a fan of...", you just say you support them.

You won't find me defending Bungle on many things, but in this instance, I think that suggesting someone who's been around the country for the past 40+ years may not be a supporter because they may be negative whilst they're there is absolute nonsense. If you have to consider as literally as you have suggested then the argument is there that 40+ years home and away is financially supporting the club, but again that's just far too literal for what is essentially just an argument about the semantics of describing a football fan/supporter/etc.