Aside from holding a pregnant woman hostage and hiring someone to kill Hayden Barns years ago, Nikolas hasn't done any real damage like Esme has. Now that her memory is back, she can take Ace and leave and no one could stop her. And apparently the writers have dropped the plot but it was hinted at strongly that Esme had something to do with her adopted parents dying.
I don't agree with what Spencer did but knowing ALL the havoc the old Esme wreaked--he chose his father over her. I think he was moved by the emotional moment they shared and how Ace immediately warmed up to Nikolas.
I get your POV but that's how I see it. And as for Laura, yes--the baby is being taking away from her as well but I have been giving Laura the side eye for months now. She is Esme's biggest cheerleader and that's just bizarre seeing how she was literally used as a weapon against Spencer/Ava/Nikolas. There is nothing wrong with giving someone the benefit of the doubt or a second chance but Laura (whom I love) has gone overboard where Esme is concerned.