Oh, great. So if an article on mises.org says that blackmailing IS aggression because its against your property, then murdering is OK. If on the contrary it says that blackmailing is not an aggression by itself, then murdering is not OK.
Mind-blowing indeed. Some of you love a tad too much your books, there is people that adores their constitution (or their favorite Rothbard book) just like Muslims blindly adore their Coran or Christians their Bible.
Logic != faith.
One concludes blackmailing is not an aggression after following a long series of logical deductions - that will not be found entirely on the link I posted, it's much longer than only that - not by blindly trusting the tales of ancient book that supposedly contains the words of a super-powerful divinity.