I'll start with this. I fully agree with your premise. People should not be contacting players/recruits like that. It's not a bad look. It's a HORRIBLE look. But people seriously suck. That isn't gonna stop anytime soon.
No one can control social media. The whole thing is an unmitigated disaster.
A couple more thoughts.
They chose to be on Social Media, right? This doesn't apply to all, but IMO the whole promoting their "brand", "respect my decision", "top 15 teams list" attitude as recruits just sets them up. You wanna be a celebrity and "up your followers", but you can't deal with the negative.
They all want to go to the league right? Get used to fans heckling. Again, social media creates an obviously larger opportunity for fans to voice opinions. Feelings hurt? Get off social media or develop thicker skin.
Oh, and they are 18-22 years old. They aren't young. They just lack life experience. I've had more than a few friends that age who gave their lives for their country without a second thought. Truly amazing what young people are capable of.
Life's tough, be tougher.