system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 how can a man who isn't a child's biological father be forced to pay child support

Aside from adoption of course.
gpt
The priority of Family court is not being just or finding out the proper paternity.  The priority is the welfare of the child.  So if you have provided for the child for years and the child depends on you financially for their well being you have to pay.  The court doesn't are if you were lied to it cares that the child is being taken care of.