It's nothing new, especially with the birth of forums in the 90's and the creation of twitter really blew it up.
I get where he's coming from but it's a side effect of playing in the NFL and the biggest team in the NFL, where millions of fans watch you/track the teams year round. Some fans get too into it, and make comments that they would never say in person but that's the internet for you. I'm guilty of it as well.
OTOH
Unless he wasn't a fan of the NFL growing up, there's no way he was perfect and never made comments about a player sucking or wishing the team moved on.
Even Dak made comments about Romo on twitter years ago before he made it to the NFL. Does he regret those comments? Probably, but it's just fans being fans. Anywhere you go in the NFL some fans will make comments players may take personally if they read them. No one is forcing a player to either play in the NFL or read social media comments.