At this point, post-J Allen Brack response, I don't even see a moral problem with running or playing on private servers. I consider it analogous to abandonware.
Blizzard are free to open their own vanilla servers and then I will switch to those and start paying again but until such a time they will not recieve a cent for me playing their game and I will not feel any guilt over it.
#theymightthinkitswrongbutitsnot