No.
You have a kid, but it's your decision.
Sounds like she's trying to skip the part where she fucked up and she should apologize to you and give you some space. Instead she's leaving you an impossible choice.
But you can talk to your son and tell him how much it stings and that you just can't do it. Sure you can "put all the bad blood behind" but it takes two for that and you can't force someone to reconcile by pressuring them with their son and luring them with a paid for vacation.
This makes me mad for you, this is so unfair. No one has to take that offer, and your son will understand. Maybe your ex will understand too, but it looks like she's still too immature to understand right now.
Yeah I think hate is a draining and destructive emotion.
There's situations where it should be used, but it should be used wisely. For example, it takes an insane amount of shady behavior to get under my skin, but when people do, they earn my hate and that makes me set very solid boundaries. But it would be bad to destroy friendships for hating someone because we got on each other's nerves for a while.