That people seem to accept this particular conclusion unironically boggles me.

People seem to forget that the Wakandans are not lead by Steve Rogers, they're lead by their King T'Challa who doesn't really have any obligation to help Steve and Vision at all if you think about it. T'Challa offered their help because the Wakandans are decent people like that, and when some assholes from space trample on their lands, I really doubt they wouldn't fight even if the Avengers weren't there. The Wakandan's warrior culture also would make them see this battle less as a 'sacrifice' and more like a duty to be performed.

Steve himself didn't make the decision to "sacrifice" Wakandan lives in that battle, T'Challa did.