Self immolation is not a typical human behavior. The monk's protest was remarkable because of this fact.
Neither is building bombs or desperate cannibalism or running a hedge fund, but for some reason those activities get brought up as evidence of "man's true nature." The reigning view in anthropology as far as I can tell is that we, for whatever reason, are really invested in the idea that humans are quintessentially violent and exploitative and greedy. When people do those things, instead of saying "hmm, I wonder why?" we say "oh, of course, that's human nature." When people help each other (or burn themselves in protest) we say, oh, that must just be an exception. There must be some underlying greedy explanation. The reality is, humans are fucked up, and also love helping each other, and those are both parts of the human animal.
One of my favorite psychology experiments went this way. They left a preschooler alone in a room with a box of cookies. In half the cases, they gave the kid a big speech about how much shit he was going to be in if he ate the cookies-- they weren't his, and we KNEW he was a bad boy sometimes, but he'd better not eat them or there'd be hell to pay. In the other half, they told the kid how he was such a good boy, and we know the cookies look good but please don't eat them, because they are for the whole class. The kid in the second case was way less likely to eat the cookies, the kid in the first case almost always ate them.
Some people end up more one way or the other.
(and some socioeconomic systems teach us horrible lessons at a young age and warp our every impulse in the pursuit of cash, destroying lives and societies and making us all into dicks)