Of course the players want to be treated with respect, just as anyone would. Respect has to be earned though. I think we can all agree that fans shouldn't be voicing their opinion of a players quality while the game is going on, but I think it's unrealistic to expect fans not to. I also don't think we can stop anyone from doing it.
As for your example with Tesco, Tash, it doesn't really work does it? If you are unhappy with your superstore you go to a different one. Tesco isn't reliant on keeping a few hundred people happy. Football is a much more captive audience situation. It's more like people protesting against politics they don't like because they don't have the option to go anywhere else. This is why we get protests against destructive chairmen. As for the swearing being illegal I think you are right, I think it is illegal to be abusive at the least, but I don't think it's really enforced.
OCM, the players are there representing the club to the public, if people want to complain about them then I don't see who we are to stop them. If my job was to represent a group of people who are funding my boss and I did it badly I would expect to be told so by the group of people whom I am representing.