I voted 'Somewhat important'.
First; as those who know me know; I study aikido for the interesting tactical - not necessarily SD - aspects. That said; I personally believe aikido to be highly effective in an SD role if
the user is effective.
OK; that out of the way; I voted 'Somewhat' for these reasons: 1) If we're talking about an SD situation (which is what the question asks), the attacker's welfare is by necessity less important than my own. However; an attacker comes in a wide variety of roles. It can be a full-out full intent assault; or a guy trying to start something, or a drunk that needs help to a taxi. Or it could be a troubled or autistic teen. While my welfare is more important to me than theirs; based on the situation their welfare's importance can go from 'not at all' (as in a full-out assault) to 'somewhat' (as in a guy trying to start something) to 'damn near as much' (as in an autistic kid). So how much damage is done to an attacker depends on the attacker. If he's swinging a weapon (such as a beer bottle - let's not talk about knives; they're a whole different ballgame); I will
break the attacking arm if that technique occurrs; i.e. I won't try to turn it into something less harmful. Why? Safety - mine. OTOH; if it's someone who really doesn't mean it; who doesn't know his own strength or needs help; I'll do everything in my power including
taking damage to keep him from harming himself - or me; more than I can avoid. So my answer would be "3a - depends on the situation"; but since that wasn't a choice; I chose 'somewhat'.