Kirk undermined entire civilizations just because his ship was in danger. You think a little private property is going to dissuade him?
Not at all but he wasn't talking about destroying property.
FLINT: If you do not leave voluntarily, I have the power to force you to leave or kill you where you stand.
KIRK: Kirk to Enterprise. Mister Scott, lock phasers onto our co-ordinates.
SCOTT [OC]: Aye, Captain, all phasers locked on.
KIRK: Mister Flint, if anything happens to us, four deaths and then my crew comes down and takes that ryetalyn.
FLINT: An interesting test of power. Your enormous forces against mine. Who would win?
SPOCK: Mister Flint, unless you are certain, I would suggest you refrain from a most useless experiment.
He's willing to kill Flint in order to take something that he has no right to take. He could even beam down to another part of the planet, assuming that the rytalin isn't just located near Flint's house. He's not just willing to commit theft, he's willing to kill when it's unnecessary.
Kirk's a criminal multiple times over. I was just pointing out something that is often overlooked in this episode. For all his talk about how mankind has advanced he's still a thug when he's prevented from getting what he wants.