libertarians and property

I've been reading the excellent mutualist blog. In "Rothbard on Feudalism and Land Reform," the author highlights the key problem with libertarianism.

I agree with libertarians that all the world's problems can be solved if we start from an absolute belief in property, but I disagree with them over their definition of property. I find their definition to be irrational (it has no philosophical basis) and corrupt (it rewards thieves). Rothbard's story show the corruption: if someone obtains land by violence, or the person they bought it from obtained it by violence, most libertarians would say the person can keep their ill-gotten gains After all, isn't that how America got its lands originally?

That is why I cannot be a libertarian, even though my views are libertarian in so many other ways.