Dude. There are a multitude of reasons why he might want to travel alone. Whatever those reasons may be, the act of doing it is in no way stupid. He was on one of the most populated hikes in America. Read the first line of this trail description. 3 million people a year and there are all of about 4 hikes in Zion. Sure it can be exceedingly dangerous in bad weather, but he checked the weather beforehand. There were a multitude of people along the way. Look at the pictures. If this was some random and difficult hike in the backcountry I would be singing a different tune. But it's not. The risk behind this hike was small. We all take on levels of risk that are acceptable to us. Any of the things you mentioned can happen anywhere. Anyone with half a brain, when attempting something solo, adds up the risk levels, and says "yeah I can deal with that". He did a fine job of that and came out ok. Jumping off the rock was fucking stupid but everything else was alright. There's no need to discourage people from being so risk adverse.
"There's no need to discourage people..." Interesting you read that meaning into my question. I was always trained (Boy Scouts, etc.) that you just don't go into the wilderness alone. Bring a buddy. I know there is a whole culture of solo hiking. Sure. But every one of these people is making some value judgments about their safety before they step out of their vehicle. I asked an honest question of how he'd done the personal math. I didn't discourage anybody from anything.
An honest question wouldn't have been prefaced with statements such as This is, like, the first rule of stepping outside of civilization: Don't go alone.
or Is it just young white dude hubris? Or were you trying to prove something?
An honest question wouldn't include against all the advice of people who do this a lot, and common sense
in the very question. You're leading someone to answer the question with guilt. I would absolutely consider this to be discouraging wording. I'd guess that this is why ButterflyEffect called your response "preaching and antagonizing". I personally agree with him.