Firstly, it's debatable whether Mourinho disrespected him. For starters, no-one knows what goes on behind closed doors. However, if he did call him a 'virus', which has not been meaningfully substantiated, then it was after one of the most unprofessional performances that you are ever likely to witness. In that context, Pogba could reasonably expect some criticism.
In terms of whether he didn't value him, Mourinho was the manager when United paid a world record fee for Pogba. And he continually defended him when he was criticised for mediocre performances.
Regardless of this, it is always Pogba's responsibility to turn up and try his hardest. This is incumbent on any person in any job, let alone one of the world's top footballers. You can't have everything all your own way in life. You have certain responsibilities, and if you don't accept these responsibilities then you will attract criticism, particularly if you make yourself a massive public figure as Pogba has.