We cannot decide that. A person should delete any kind of reviews or not is his/her decision.
While I get your frustration, I can't say much because I do not know what kind of a review you had dropped.
You read. You didn't like. You wrote a review stating the same. Your job is done there.
The writer read. The writer didn't like. He/she deleted the same. Her job is done.
Look honestly, I have got no reason to defend anyone and I won't do that either. There are a bunch of things in the world that we do not like. Again - that doesn't mean that they aren't good. (The reference is general.) They maybe good. They maybe not. It's a subjective thing but do we get stuck on something that we don't like? No, right? We move on and ideally, we should because that's not our stuff to change.
A couple of things like the writer should be ashamed of not being able to accept the criticism is quite disappointing to read. You went too far really. At least that's what I feel. Come on, people. As humans, we have different capacities and capabilities. Not everyone can deal with criticism well. Not everyone can deal with negative comments well and it's okay. Sooner or later, everyone learns. Life has a way of teaching everything to everyone! Besides, we cannot force and teach someone who isn't willing to learn. Let everyone learn at his/her pace.