Sometimes arguments like this make sense - some systems do have basic assumptions which render them invalid. But usually it is just a way of dishonestly avoiding argument, especially in arguments that have two characteristics to some degree:
a) You feel smarter than the person you are debating
b) You can't quite grasp their argument but as a consequence of 1), don't want to admit it. Thus you change the focus.
I was reminded of this when reading this Ayn Rand quote in an essay:
“[t]he entire apparatus of Kant’s system . . . [rests as] on a single point: that man’s knowledge is not valid because his consciousness possesses identity”Perhaps unsurprisingly, Rand is wrong.