Assuming that there's not more than one dire wolf/bat outlander, it looks like attacking Fortress peeps is this guys modus operandi when he's got no Tribbies to bump uglies with, so...

Your question kind of doesn't make sense. As a goodie, it would be bad form not to protect a groupmate if you could. Likewise, I would say the bigger question is 'Why wouldn't he get involved?' This outlander attacks other fortress peeps and attacked a groupmate, who fled and duoed and then the guy attacked him. So... before you go getting angry at people for pointing out the obvious, remember that just because you say something like, Aside from the obvious reasons, why did you get involved... that doesn't invalidate the obvious reasons as being plenty reason enough.