Wow. That is just so uncalled for and so rude. I always like to think of this quote "Before you speak ask yourself if what you are going to say is true, is kind, is necessary, is helpful. If the answer is no, maybe what you are about to say should be left unsaid."
That person definitely did not ask himself those questions! And, like you said, that could push someone over the edge.
What about staying in a horrible relationship? How is that for the kids?
You can't comment stuff like this without knowing the whole story or in general. I had someone that was nasty like this to me and I am so glad that I blocked them.