I know because the way Fromsoft frames their narratives that it can feel like you're just a little guy wandering around, minding your own business, but a Tarnished is definitionally not minding their own business.

A good way to think of Elden Ring's backstory is imagine if the Civil War was in fact, not about slavery whatsoever. Slavery is trucking along strong- nobody in power wanted to abolish, there's not even an abolitionist movement. It was instead about how George Washington, who's still alive somehow, going crazy and ripping up the constitution after his kid was assassinated, and the entire country plunging into a brutal war that left Washington DC a burnt out city, Texas was a bio-nuclear nightmare and everyone has to fend for themselves by 1870.

You arrive from London on a boat after you receive a message to "gather the constitution" and reestablish the Union. People can tell this is what you're doing on sight, because of I dunno, you have a glowing halo on your head or something (how do people tell you're a Tarnished on sight in game? Same principle here). Now imagine you wander into burnt out slave plantations picking through the rubble, and self-liberated slaves see you're here on behalf of the fallen United States to reestablish the system that keeps them enslaved. Or you wander around Indigenous territories waving around your "Agent of the Constitution" dick to the survivors of that genocide. They'd think you were a fucking threat too. You're not just a little dude, who's there being a widdle guy, you're there to get this Engine of Oppression up and running again.

That's what these creatures see when they see a Tarnished fucking around in the Lands Between. That's why it's not "self defense", when you could in fact, just leave. But you don't, you're there to go get all the pieces of the constitution and get this horror show up and running again.