Then the cost of their well-being is money. If that deters you and you WILLINGLY give up the chance, you are choosing wealth over the wellbeing of your children. If your ex is that evil and vindictive then they need you MORE, not less.
Morality is not subjective, nor is it changed by circumstance. Morality exists precisely for guidance in murky situations. People can choose to be immoral and rationalize it by circumstance but that does not excuse or change the immorality.