The practice of "serosorting" is not really anything new - it's just that modern testing methods have made it easier. That said, anyone who barebacks *should* know that they are taking a risk, no matter the attempts to reduce it. Like Rawtop said, it's a numbers game. I don't condemn anyone who goes to extreme measures to limit their exposure to a still potentially very dangerous disease. I do it, to some extent, myself. But, I also understand that what I do is risk mitigation, not risk elimination.
I think the vast majority of people on here, though, would rather not have sex than have sex with a condom. Not having sex isn't really an option for most humans, so that leaves risk mitigation. It's up to everyone to decide what their level of comfort is, from all-on bug chaser to "serosorting" to "safer" sex to life-long celibacy and all the stages in-between. I think people tend to forget that life is all about risk. Participating in the road kills a lot more people than HIV. I wear a seat belt, but I am not willing to have a helmet and head-restraints in my car like a NASCAR driver. Similarly, I top only (not because of risk, but because I just am a top), I don't fuck guys with 15 random loads in them already, etc. Still, I could get killed by a drunk driver or contract an STD. It's called life.