I think it depends on case by case.
If we see the life story of Thich Quang Duc, his self-immolation can be seen as necessity. http://en.m.wikipedia.org/wiki/Thich_Quang_Duc
Due to his self-immolation, Buddhism still exists in Vietnam.
Self immolation can be seen as the bodhisattva act depending on the motive.
Self immolation in my opinion is very different with suicide, where that act is ignorant act.
On paper, boddhisattva should be ready to give his life anytime and anywhere, when it is necessary, and such act is not viewed as ignorant act.