I think SOME people (at least younger ones) when they think of "socialism" don't really associate it with communism or Marxism. They hear the word, and think of it more of like, social security, Medicare/Medicaid, and various government programs to help those in need. I think that's what people mean by "social democracy/democratic socialism". They're not actual "socialist-socialists", just ignorant.
OR, it could be just a case of language evolving. That happens too. Like the word "liberal", for example. What people called "liberals" in the past we now call "libertarians". Maybe that's what it is? I'm guessing someone who studied linguistics would know better.
As for those who call themselves communists, they're fucking idiots, plus many of them didn't grow up during the Cold War -- to them it's an event that happened "Ago", and you had the whole Red Scare bullshit, McCarthyism, etc. Nowadays, most communist countries aren't really the BIG THREAT that the Soviets were. China's fucked up, but it's not the same. Also, Vietnam had a lot to do with it as well -- let's face it our government DID fuck things up when it come to "fighting communism". We certainly weren't innocent, at least when it came to foreign policy. (And this isn't a "liberal vs. conservative", since both sides were doing it)
But for the most part, once again, it's ignorance. And they haven't actually LIVED in a communist country, or known anyone who has.
And for those who do know all of this, but still consider themselves socialists and/or communists? Well, there are neo-Nazis around, what's so weird about neo-commies? People are assholes.
(BTW, anyone here actually read Marx? Dude was a total crackpot, but as one of my professors said, his solution was fucked up, but he did indentify the problem correctly, at least for that particular time period)