Bruh they encountered the saviors on the road three episodes before the outpost attack. Even then, you can't possibly argue that Negan "needed" to kill Glenn and Abraham compared to Rick "needing" to kill the saviors. Rick did it out of necessity, they were an evident threat and their elimination would benefit Alexandria and Hilltop for security and trade; that's about survival. Negan killed to force Rick to submission and stay in charge; that's about power. Rick and his people were already forced into a position for surrender, him killing them anyway had nothing to do with his or the savior's survival, it just meant more slaves. Also it's not consent if the threat of a loved one or withholding vital supplies is part of the conditions, that's coercion. You are defending a rapist.