I did say I realise it's a different reality riding in a place like that. I probably wouldn't ride a bicycle were I American.
It isn't really my cup of tea, I can appreciate the riding discipline but at the end of the day it is making a lot of unaware people participants. I don't really like that. At least other riding disciplines that push the boundaries have organised events.
I also wouldn't go mountain biking*
*may be due to geographical circumstance
The U.S. is a hugely varied experience. For all the city traffic war zones, there is an enormous, bewildering, amount of wonderful rural cycling. A bewildering amount. Everywhere. You could live a thousand lifetimes and never scratch the surface.
Legislation may be the only way to curb the behaviours on display in some of the associated material featuring these fixie fools. I have a huge issue with the Strava twats turning cycle ways into their personal velodromes. There is a case for 'extreme' riding, but not, as you say, obliging others to follow suit.
I have aggressively defended my road position when it was prudent, and confronted dangerous driving practises where possible, my entire cycling life. It makes no sense to relinquish all that knowledge and experience, lived experience, to the notion of cool, entertaining, hip, rad, gnarly, sick, or whatever attributes are bing applied to practises which lead to further polarisation between cyclists and others.
I am no less of a cycling activist for seeing all this for what it is. Marketing.
Which neatly brings me to your remark about mountain biking. Worry not about the flatness of your lands. They are a country mile more mountainous than the tarmac city streets the vast majority of 'mountain bikers' negotiate day to day.
The mountain bike, equipped as it generally is with decent to excellent all weather braking; sturdy wheels and tyres that cope well with the rigours of the urban roads, and a seating position that lends better visibility than the drop bar brigade in their best control positions, is ideal for the commute and general work around the hustle and bustle of the conurbation. It could as well have been developed specifically for this purpose, but then marketing..