I find it personally amusing to look back on my life and how vehement I have felt at times and how ridiculous my positions were in retrospect.
The example that I have in my mind in particular today is how I felt pre-20. I was so against kids that it's unreal. Putting it succinctly, I had this belief that someone being the son of a drug addict would necessarily imply that I would both be an addict and additionally that I would similarly pass it on like some kind of unending transitive relationship.
I remember quite vividly thinking to myself that if I could only bring myself to tolerate the concept of gay sex that I'd be a lot happier as a gay male. I've never particularly felt the need for social approval or participation, generally speaking I did and do prefer "stereotypical male" company, and as a rule I've found that the gay friends I've had over the year have frankly been a better class of people as a whole than my straight friends. The thing that I didn't get pre-20 that I understand as a somewhat more mature adult is that if the thought of giving or receiving male-male sex turns you off then you're probably not gay, as much as you might like to pretend that it would make your life easier. (I suspect it wouldn't) Also I didn't know enough about statistics to recognize that a relatively small sample size generally speaking implies that inferences based on data are shaky at best.
I remember arguing against the theory that the purpose of life was to procreate. To be honest I find myself re-thinking this one lately as the days go by and my progeny approach reality in a IRL sense.
One thing that I do believe is that people are hella crazy and that ultimately the only partner that ever works for a person long term is one whose version of crazy offsets your own. As a married man I still think this holds true. My wife, at times, can be the most indecisive person in the world and similarly, at times, I like to be the one making the decisions. She's the type that will take 10 minutes to pick out toothpaste from the aisle whereas I'm already at the checkout as I've preplanned every step I took before I arrived at the store. Similarly I am bad with common sense things whereas she is very down-to-earth and logical.
I don't know that I believe that marriage is required for people to be happy and I don't know that I believe that everyone needs to have kids. For me both are/were very important to me but I'm willing to accept that my view of the world is not everyone's. Heck, 10 years ago I would have totally disagreed with everything written here today so who am I to say that 10 years from now I won't similarly re-read this with disgust. :)