Well, this is quite something, isn't it?
I can't blame you if you're surprised; it's not every sport that explicitly encourage physical pain. But I get it if you're not surprised, too; there's an awful lot of sports that try to look the other way at pain.
We the fans certainly complicate matters. We hate to see "head hunting" or "targeting", but we love big hits. We love "giving the other guy something to think about". We love seeing a player rise above the pain. And our list of "Dirtiest Players" often grows one shorter when our team picks up certain guys from free agency. I mean, I've certainly rooted, mostly in jest, for Tim Tebow to break a collarbone, and my opinion of Dan Carcillo certainly changed when his uniform did (though it's back to normal, now that I know he's useless).
There is a difference between enjoying a strong, physical sport and just cold baying for blood, but man, I'll admit that that line is only a molecule thick in some spots. Hockey is instructive here (and as this blog goes on, we'll definitely talk more about that); I really can see a moral difference between checking and fighting. But there's checks and then there's targeting the head. There's fights and then there's scuffles after the whistle. There's a lot of grey area, and I don't envy Brenden Shanahan in sorting all that out.
There's no real bright line rules to guide us in those closer cases, and I can't really propose one here. But maybe I can suggest a frame work to get us thinking about this.
I think the question is intent. If a player is intentionally trying to hurt another, or if any sport or rule explicitly encourages hurting a player (even just to the extent that he's drops the ball or fumbles the pass or misses the puck or whatever) it's suspect. There's still a lot of gray area, and some sports I love are probably implicated. Bt it's a start.
I think it's clear how Ultimate Tazer Ball runs afoul of that standard; the defense's entire means of accomplishing it's goal is physical pain. I know there's only been minor injuries so far, but man, that seems like walking the razor's edge.
Of course, I can only speak to why I wouldn't watch such a sport, and why I would tell other people not to do so, either. As far as participating in it goes, I really have little interest in denying someone their right to fuck up their own body. But as far as we, the fans go...well, at a certain point, we just start to look too much like Romans.