Earlier quoted context omitted.
I still don't understand why that's a bad argument. In context, it's generally used to oppose hard leftist ideas (Marxism, etc). It's rarely a criticism leveled at reasonable reform or change; more when it nears outright revolution. In that case, it's not an unreasonable criticism.
It's a bad argument, because validity of a critique is not predicated on critic's life choice. It's like arguing that you cannot critique a movie because you have never made one.
If we take a common example of how I've seen this play out:
A: iPhones and Apple are evil because they require child slavery.
B: But.. you own an iPhone?
A: Oh so I'm just supposed to go live in the woods?
I don't think B supports child slavery. B is pointing out that even people espousing this idea participate in the system because the alternative (not owning the iPhone) results in a worse outcome.