I think maybe the people who are saying they'd ditch the kid don't have kids or young relatives or something?
Like in this situation you're not talking about some hypothetical. You'd be talking about a kid you have raised since they were a baby. Who you should already love and care for. Of course it would hurt. But this kid who you love didn't do anything wrong.
I don't get how someone could have an affair and have a secret love child. But I also don't get how someone could completely disregard their child even if this betrayal was found out. Being betrayed doesn't shut down your feelings for your family and it also doesn't mean you get an out for being a father who raised a son or daughter.
I have two kids with my wife right now that are, as far as I know, are mine. If it came out that she had conceived one or both of them secretly while cheating on me, I don't think I could ever acknowledge them as my children again. That well would be successfully poisoned by the betrayal and decepion. It would be heartbreaking, but it's an unfortunate reality.
I just don't get it. Surely you love them by this point.
Likewise if you found out you weren't your Dads kid you'd be fine if he didn't acknowledge you as his son anymore? ---