User blog comment:TheDoctor230/Barry Hasn't Defeated a Big Bad Yet (Technically)/@comment-26537965-20180110135435/@comment-24152851-20180114234902

^To quote Barry "back when you were me" Key word is were. They have the same past, but different futures. Time remnants can act as extensions if they're personalities are unchanged, but sometimes they gain individuality and split off. The fact that Savitar opposes Barry, means he no longer has the same intentions and motives. He's okay with ruining the life of Barry Allen, because as far as he's concerned that's no longer his life.