If you were in a military unit under heavy fire with half your unit split between two defensive positions and the enemy was gaining on one of those positions would you really want your buddies at the other position to drop a hand grenade on you just to hit the incoming enemies?
It'd be seen as either a betrayal or a major error in judgement, not as 'taking one for the team'.
I suppose my logical imperatives override my general empathy on this one.
The danger involved to the character's is what I find important. To make an analogy I feel is slightly more apt and less obviously condemning, I'd say "If you were in a military unit under heavy fire, and your unit was split between two defensive positions, and the enemy was advancing towards a city that wasn't yet finished evacuating the innocents, would you want your allies to watch the enemies crush your divided group and destroy the city, or would you want to call in an airstrike on your general location and pray you don't get killed in the bombing and can mop up the remnants?"
The adventurer's (generally) are doing these adventures to help people. And even if there are no innocents at stake, as a human being, if people I cared about (the party who I am 'in it together with') were going to die if I worried about my own safety, in a world where resurrection is possible, I'd probably say, "Blow me to kingdom come! You all owe me a year's supply of beer!" Or something, sacrificing myself for the betterment of my group.
It can be a somewhat personal thing. Myself, if I was asked permission beforehand, I might just okay it, if I could analyze and agree it was appropriate. Even if In Character, my PC wants to choke the person who did it until their eyeballs pop out. I'd simply inform the person how my character would react in character, and say, "I agree this is the best place to hit, and will drastically ease party resources. Do it."
But that's just me. And some people would say I'm a powergamer... which I find somewhat ironic, since most of my 'RPG' experience is almost entirely roleplaying with no 'mechanics' at all. (Which got frustrating when other players would try and fight me... it was like playing Cops and Robbers as a kid... 'I shot you!' 'Nuh uh! I shot you first!' 'nuh uh!')
Hm... I'm up too late, and now I'm rambling. [/ramble]