I have noticed this. Messi and Ronaldo are both great players, and they have their own strengths and weaknesses. In order to become a Messi fan, you don't need to hate Ronaldo (and vice versa). And I don't think that there is any personal hatred between these two players. The fans need to understand that. All that said, IMO Messi fans who hate Ronaldo are more common than the other way around. And what would be the reason for this? Nothing comes to my mind right now.
Lionel Messi is undoubtedly the best player, but Lionel Messi's career has had bad times and he has decided to retire several times, but he has come back from those bad performances and has made the team the champion of many big tournaments including the World Cup and Copa America. However, if Ronaldo is compared with Lionel Messi, then in some ways I will put Cristiano Ronaldo ahead of Lionel Messi. In football, Cristiano Ronaldo is a full package in which you get everything in full. Cristiano Ronaldo has worked hard to reach this level and he has never received team support, yet he has made the team the Euro champion in one season, so his contribution cannot be forgotten.
I don’t enjoy taking part in the Ronaldo and Messi debate. Between the two players, I believe Christiano Ronaldo is the best and I’m not rating them based on just goal/assists stats or Ballon d’Or won. I’m comparing the trajectory of their career, Ronaldo won the Ballon d’Or while in Manchester United and in arguably the toughest league there is. Messi won his Ballon d’Ors with Barcelona, he played with legends Ronaldinho, Iniesta, and the likes… so he had an easier path compared to Ronaldo while Ronaldo had to make his way.