Keegan is young, and he is only fanning the flames by saying publicly that it bothers him.
As stated already, consider the source - the haters have psychological issues - they need attention and/or envy a pro golfer's life and lifestyle ... it's their only way to "get back" at people who have what they do not have. It gives them power.
So - my advice to Keegan is to take away that power - ignore them - be happy within, and don't care about haters. And that advice is the same for all of us - have the wisdom to learn, know and understand yourself, find happiness within, and it doesn't matter what outsiders say. Don't give them that power over you.
As I said, Keegan is young. The process is sometimes a long one. Most never learn, some strive to learn and succeed in various degrees.