I like them and am very disappointed that they are so frowned upon.
I think it is unfortunately a vicious circle: because they are frowned upon, it's mostly rude if not injurious people who still make some, so it's (understandably) being even more frowned upon, etc.
Now I understand the reasons of people who don't want them; I just wished it was not so taboo that it is almost impossible to get any critique even vaguely solicited (for eg. If one says they are open to critique, this is often not enough. I only manage to get some by explicitly asking in dedicated threads (which sometimes even get derailed by anti-negativity people...).).
Truthful (and, at my stage, often harsh) critique is my main way toward improvement. I'll take solicited and unsolicited all the same, as long as I get SOMEthing 
Now even if I like it, I do see some annoyances that are coming with the unsolicited kind. For eg. I am fully aware of my horrid anatomy, and I'm workimg on it, so I would notify people I already know about the problem, in case of a solicited critique. An unsolicited one pointing out only my anatomy issues would be useless unless it gives new ideas for studying it, but whatever. Another one pointing anatomy AND something else that I was not aware of will be received as a nice present!
Also, I did the DM thing before learning it was a no no in the art community, and that was actually to avoid embarassing the person in public in case they were not comfortable with receiving the critique. I now use it more carefully, but that means less communication altogether as I have difficulties with social politeness if it is not exactly my feelings.