At a guess I would say it is the tennis version of sledging.  It can do a great deal of harm to a person's self confidence.

While I think Sharapova's reaction is a bit offputting at least she is not letting it get to her.

As the authorities have deemed she has served her time the other competitors will just have to accept it, but I do feel that she should be doing the hard yards to get back into top competition again.

She is a good enough player that it would not take very long.