Logically! The question is, [where does pure-subjectivity leave us] if there is no objective absolute standard and our beliefs are different regarding the same subject matter?
That is why we have conversations.
Ideally we can persuade each other with logic.
When logic fails, we use enticements (which creates [de facto] mercenaries).
When enticement fails, we use fear-mongering (which creates [de facto] cowards).
When fear-mongering fails, we use credible threats of violence (which creates [de facto] slaves).