I don't think that they believe it is idolatrous to support a football team or wear the colours etc especially not in the UK
We don't have a cheerleading culture here or a parade/pageant culture either. And although the National Anthem may be played at major finals or international games football isn't associated with patriotism at all.
We use to play "friendly" 6-a-side football every week and we all used to turn up to play in whichever teams shirt we happened to support. Everyone did it - elders included. No-one cared.
I know that this is definitely UK wide. Of course there would be individuals who held an opinion but they actually just didn't like football. The WT may have posed the question "Is this idolatry?" In reality no-one thought it was!