There’s a lot of talk about Keith’s suicidal tendencies after that last episode. The suggestion is that he doesn’t value his own life AT ALL, but I really didn’t read it that way.
He couldn’t see another way. There was no one with enough fire power to break through the shield, and he was desperate, absolutely DESPERATE to save the lives of Shiro/everyone he loves.
He waited until the LAST POSSIBLE SECOND to make the heartbreaking decision to put their lives above his own. That was an act of PURE LOVE, not self hate. He was going to save their lives or fucking DIE TRYING!