An ad hominem attack is used when there are no rational arguments remaining to support your position. This is when you attack your opponents character or personal traits rather than addressing the issue at hand.
There are many politically correct progressive busybodies who use this method to silence opposition to their attempts to reengineer society to what they think is best. Among many of those issues today are:
These are issues that you dare not disagree with, dare not oppose or you will be ridiculed, denigrated, and made to look like a bigot. The people who have fallen for these issues will attack you relentlessly until you either concede or leave. They have no rational arguments on their side. All they have are assertions with no foundations. They function in every way like a religion. They are ideologues. Their ideology is accepted on faith by the members.