All right so my friends and I always seem to get in a heated argument about the death penalty. I personally think it's wrong. But between the four of us, I'm the only one who seems to think that way. And it's not like I'm trying to force my beliefs down my other friends' throats but I just don't feel like they respect my opinion. The three them feel strongly that it's right and I know that it pisses them off that I'm the only one who disagrees but one thing that they do that makes me feel disrespected is when they gang up on me about it. And it's really hard to argue with them and defend my statement when they're all verbally attacking me about it all at once. So I always try to avoid the conversation as much as possible because it's a touchy subject and I always end up losing. But every time we're around other people we know, they always seem to bring it up and ask another person"So what do you think about the death penalty?" and most of the time when it's brought up, it's completely random. I feel like the only reason they bring it up is because I'm around. I try not to say anything and wait until the subject is changed but it really pisses me off. Am I just being too defensive? If not, how can I tell my friends that it makes me feel disrespected when they do stuff like that?

You're not wrong, just a different opinion, no one can win. Ask if they are doing it just to piss you off. If they say No, then they should stop if they are your friend. If they say yes they are trying to piss you off, Tell them NOW you feel their should be the death penalty for people TRYING to piss you off.
Some people are just jerks.
Just noticed your name, I see why you wouldn't want the death penalty.

Stop allowing the topic, if they bring it up change the topic or relocate, tell them it is no longer up for debate. If they can't understand that, then your 'friends' aren't very friend-like and I would be looking for some new people to be friends with.