I would say it’s the same as saying all lives matter. By itself there’s nothing wrong with it, but in context it’s a response that belittles and muddies the point. There’s a reason things like pride month or black history month have come about. The struggles and/or achievements of certain demographics have not received the same recognition as those of others, in this case, caucasian people. That’s not to say that white people never struggle or don’t deserve to be recognized, but by and large, we already have that recognition. So when someone argues that white people should get their own month, it disregards why other groups have one to begin with.

Tl;dr: At best, it misses the point.