The Hebrew word here describing the damage done to the genitals is dakkah
- meaning mutilated or wounded. Although some suppose that this can refer to an accidental or genetic defect [Merr.Dt, 307], the context and the difference in language from Leviticus suggests that this isn't a case of someone who has been through an accident or a fight and can't help what has happened
Rather, as our socially-informed commentators tell us, this most likely refers to someone who has wilfully and purposefully damaged themselves, probably as part of a pagan religious ritual. And this is right in line with a theme of Deut. 23 itself, which forbids various foreigners from entering the assembly: The only person who would undergo such treatment would be a foreigner (in pagan practice, deformity was "not only acceptable but frequently central to the practice of the cult", as for example were the assinnu of the Babylonian rituals - Merr.Dt, 307) -- or else someone who so dedicated themselves to a pagan god that they took this extra painful step to demonstrate their devotion.
Have they suffered enough? Perhaps they have -- but it would have been their own choice in the matter. It's not surprising that God declared that anyone who went this far in devotion to false gods ought to be excluded from the assembly of the true God.