Requesting a DNA means you are in doubt if the child is yours or not. If you are sleeping with one women at a time, you would know that child is yours.
Because at the time the woman took in, you were having sex with her so there should be no reason to argue if the child is yours or not. Especially, if she never given you a reason to doubt her loyalty.
Secondly, paternity test request also means you doubt the woman slept with only you during that period. In this case, you either want an excuse to dodge child support or you want to be sure you have legal rights over the child before investing your resources.
Either way, men are just as responsible as the women who commit paternity fraud. If he was doing his due diligence, he would know when the woman he's sleeping with got pregnant.
But blames aside, unless the relationship is a long committed partnership, the only way to tell the paternity of a child is through a DNA test and it should be made compulsory to dispel loyalty doubts from women who feel offended when asked to do the test.