Violence at any level is not acceptable regardless of gender, sexuality, age and race. To say that they "deserve" to be assulted (家下自食其果啦) just because they're mainlanders is simply wrong if not offensive.
No one deserves to be assulted regardless of who they are or what they have done. What I take from the article is that they are victims of a horrific violent racial crime. Full stop. Violence cannot be justified.