Utah fans don't like him, given that he's a little loud and ostentatious and that he switched to the rival. And you're right that the fans saying his family are trash are both idiots and absolutely out of line.
Their other comments are dumb too - I wouldn't even call Samson a traitor. It hurts me to see Samson in blue but I get why he switched - play with his brother, dad wanted it, he'll get used more at BYU - and I hope he keeps doing well, especially because BYU won't play Utah again this year. He gave a lot to Utah and is a good player, and I appreciate him for that.