Sadly with this attitude, you yourself are adding to the problem, not actually helping it in any way at all. We can all see that football is rife with complete morons on and off the field of play but distancing yourself from these people is the best thing you can do if you have the brain capacity to do so. No one has the right to feel they can just give someone pelters for no reason at all other than they wear a different coloured strip to the one you allegedly support or in life in general. That's just the definition of someone being a c**t for the sake of being a c**t.
You say that weaponising someones mental health is beyond banter yet slagging someone off / pelters / winding someone up is ok? How do you know its ok? If you put yourself in their position, how many times when you've been at your work has someone put you down, given you pelters etc week in week out? I'm sure that in Cox's case as with other footballers, not just at this level other than being given pelters on the pitch, i suspect that they've had the rejection of playing at a higher level and being told they're not good enough and all of these factors have contributed towards their mental health. How the individual deals with that is another thing though. Some have the mental strength to shake things off, water off a ducks back, however, in Cox's case, its probably manifested itself inside his head into something greater to the point where he tried to take his own life and this can now be used by opposing players and fans to put him off during matches.
I've seen comments on here with regard to players invite things on themselves (Bobby Barr as everyone's lower league favourite hate figure) however, he's reacting to getting it in the neck from fans and fans give it back in retaliation. It's a vicious circle and I doubt that it's going to change any time soon.
Rather than dishing out abuse / pelters / wind ups to the opposition and having a laugh with your mates about it, just support your team, you know, as a 'supporter'. As you've said, football's not a life and death situation.