@tflb1 You don’t have to support Murray if you don’t want to. Support whoever you want. But remember that there is a subtle difference between not supporting a player and actively wanting that player to lose. It’s possible that’s your friends wouldn’t criticise you if you did the former, but because you are doing the latter they are criticising you.
For example, my brother is the worst gloryhunter ever. He supports Manchester City (having switched from Chelsea in 2011) Barcelona F.C., the Spanish national football team, Rafael Nadal, Sebastian Vettel, etc. despite having lived in London all except 2 years of his life. Despite being an obvious gloryhunter, it doesn’t annoy me that he supports these teams/people. However, he actively tells me that he wants the teams I support to lose, and cheers for the other team when I watch them on TV. It’s that which annoys me more!
Btw, what makes you think Murray isn’t a nice person? Granted, I don’t follow tennis that much, but I never seen much evidence to show that Murray is a bad person.