I think one major reason the stigma remains is One Flew Over the Cuckoo's Nest. That sequence showing Jack Nicholson being forcibly treated then coming out of it completely docile scares people. Sadly, the public doesn't stop to think about the fact that it's a film with an actor trying to make the scene more memorable. Real ECT is nothing like Nicholson's portrayal; the "aftermath" is like any other time you've awakened from anesthesia. Unfortunately, Nicholson is all (or about all) people know.

I think, however, that with the educational videos available online we'll start to see a change in attitude. Although Claire Danes didn't portray it accurately in Homeland, either. There are other depictions you can find on YouTube though