I'm a bit on the fence...
You know, we're all recycled stardust. We drink water that has gone through the sewage system and been cleaned (think about that for a second or two), and we eat food that has been fertilized with who knows what. We all breath the same air. I'd be shocked beyond belief if we didn't all have some the atoms and even molecules in our body that some murderer didn't once have previously in their bodies. So? Does that make you more or less of a person?
That being said, if part of your BODY was "contaminated" in such a manner and you don't have a problem with that, why should it matter if your inanimate firearm was previously used by the same person/people whose atoms are now inside your body? The firearm itself is just metal and wood (OK, and some plastic in some cases), it isn't what caused the harm (if any) that some people are concerned about.
Another way of thinking about it is that maybe your ownership of that firearm will result in a good use of it (i.e. take out a would-be murderer, or to teach a kid how to shoot well so that he can survive a war in 15 or 20 years, raise a family, defeat our enemies, etc.).
I own several milsurps (rifles only), and I'd be surprised if none of them was used to at least shoot at another person, if not kill an enemy combatant. I do plan on buying more.
However (here's the other side of the fence), being Jewish I simply can't bring myself to buy any German weapon that could have been used in WW2/the Holocaust. I just can't, despite everything I said above - with the exception of an Israeli Mauser, which was "redeemed" (in my somewhat altered mind) by being used to preserve Jewish lives before/during/after the 1948 Israeli War for Independence (and which I'm in the market for now).
As to a suicide gun - as someone else said, it'd be a bit creepy. But if it had a good enough price...maybe.