A lot of you are underestimating Blood, he's not a mass killer who only thinks of himself, he's more calculating and strategizes the best solution that benefits Home-World or gem-kind in general. Sure he's using half truths, but because he feels that the gems aren't old enough to hear the full truth. And yes, he did plan to give Spinel more freedom by removing her emotions but he even started he may have done more harm them good, that he made a mistake. Blood is evil and his emotions get the better of him but when he has a clear head, he is just trying to help who he believes to be the good guys.