"If you removed EPA regulations on BP, does that mean they will suddenly become good citizens and not pollute anymore?" That is an example of an argument used against libertarians when the subject of regulation comes up. It contains many premises not shared by libertarians: under current law individual land owners were not able to file legal suits against BP, the state of Louisiana was not able to take independent action to protect coastal properties from the spill, and the owners of BP were not held liable for the damage caused by the company.
"If you change this one little point, and leave everything else exactly the same, doesn't that prove that libertarianism doesn't work?" Pointing out all the unshared premises, that "everything else exactly the same" is not something libertarians agree to, does nothing to those making the argument. The response, over and over, is to say that anyone who points out it is a loaded question is actually ducking the question.
Does the argument represent a misunderstanding about libertarianism? Or is it a deliberate distortion of what libertarians believe? Given the refusal to allow any discussion of unshared premises it seems like a shallow attempt to conflate the corporatism and capitalism, a conflation that can only benefit the progressive belief in a thoroughly regulated economy.
People who make that argument forget that libertarianism is indeed comprehensive. Changing just one point, the endpoint regulation that appears to be necessary because of all the prior interventions, does not negate the theory that would deny all the previous interventions as well.
That leads to another, even worse argument used against libertarianism: the Somalia argument. Given all the times libertarians object to government interventions that make the situation worse, both in economic and civil matters, those who favor an activist government argue that libertarians should move to Somalia where they would be more comfortable. The argument also implies that the chaos that takes place in Somalia is exactly what libertarians advocate.
History clearly and easily shows the truth about Somalia, in which it was the fallen government of Somalia that brought the country to the lowest point a country could possibly reach. Those in the government forgot that a parasite is not supposed to kill the host, and proved that it takes a government to create the degree of chaos normally thought of as anarchy. Once the government fell, the people started to rebuild. Occasionally some government sends in a peace-keeping force to break everything again and install a temporary government that will fall once the foreign troops leave. The resulting destruction is considered further proof of how lack of a government is unworkable.
Given those facts, then why is that argument made? Like the loaded question, it is not made for the purpose of genuine discussion. The thing to do is, as always, to point out the facts, but there is no reason to suppose that doing so will actually work. Those making the two arguments are not interested in facts, they are merely hoping that others witnessing the argument will be more impressed with the argument than the facts.