Get him in front of some other bloggers and say:
It’s liability per se that isn’t justified by libertarian standards. Under Lockean property rights theory, you own physical things, not the values of those things. It is for this reason that if you set up shop next to a competitor, you are not infringing his property rights, even if his business ends up being worth less. So let’s say I steal your painting. Yes, you do deserve your painting back. It is yours. But say I steal your painting and lose it or wreck it. That should be the end of the story. You never owned the "value of that painting." You simply owned the physical painting. You are not due compensation. If you take my money as compensation for your loss, that is simply another theft. All this talk about the "doctrine of rights forfeiture" is handwaving. The forfeiture doctrine is a convenient utilitarian fiction (which I will partially endorse), not libertarian theory. Rights aggressors do not, in fact, lose their own rights in turn. Why should they? Evreyone in prison is there unjustly and yes that includes murderers. I will, of course, accept many of these injustices for utilitarian reasons; I am a good pluralist.