This is just completely untrue. You can kill Wrex in the first game for not wanting to destroy the genophage cure, agree with Mordin and kill his assistant in the second game and doom the krogan to a slow genocide in the third game to bolster your relationship with the Salarins.
I mean Shepherd's entire thing was he was trying to save the krogan's since Mass Effect 1 all the way till Mass Effect 3 where you completely save the krogan's. And he has not just one but two krogans on his permanent Squad... so atleast that one shouldnt surprise you