It’s a mistake, I think, to view this primarily in terms of “how much immorality one can pay to paper over,” although many utilitarians are at least brought to the realisation that there might be a long-term problem with illegitimacy by that line of enquiry.
The bottom-line question is do children deserve married, committed parents, and what are the consequences of the failure of society to maintain that norm?
Of course children do deserve a well rounded family.
No doubt.