They passed a law that mutants aren't allowed to kill mutants, it's enshrined as one of the first laws of their constitution alongside protecting the sanctity of their land. These people aren't stupid, some of them are geneticists they know mutants have a chance of having a human baby, but they aren't going to ostracize their human baby because of it. It's not like mutants don't have human allies like Corsair and Briar Raleigh and others. They aren't going to unilaterally punish humans, but if they find out a racist group is preparing a mass attack against them with very destructive weapons then they are going to be proactive and try to stop the racist terrorist group from attacking their nation.