I somehow recall that was already proven as not worse in studies of children from divorced households (might have been largely equitable custody) vs nondiviorced that the answer is no even without extremes like domestic violence being involved. There are extra expenses and difficulties involved in separate situations technically but the alternative may be worse. Two separate remarried families wouldn't even suffer from the resource loss and lack of support structure assuming both have healthier relationships.

The rhetoric seems to be spread more from a mix of traditionalism and insecurity about being dumped or stuck in an unhappy marriage than solid facts.