I don't care if they're adults. I don't care if they are getting a free education. It's not right because:
1) it degrades the person giving the criticism
2) it hurts the person receiving the criticism---adult or not, privileged or not, it hurts them. Do you want to hurt? Is that what makes you feel good about yourself?
3) it damages the team. Players transfer, they leave early, they whisper to peers. It breaks down the team.
Can you think of any good reasons why we should criticize players?