When I was younger, 20 or so, I participated in shooting cruise missiles into Afghanistan. This was October 2001. I felt very righteous at the time. Years later, after reading many different books, reading the news on a regular basis, my general understanding of humanity and the world being much more developed, knowing that the military industrial complex and our politicians (most who have never served) having ulterior motives, etc... well:

1. While I still have a lot of respect for our military I really do not trust our intelligence agencies and politicians and in hindsight there's really no way to know if the things we bombed had civilians at them or not or if they were even really in need of a 1 million dollar missile being used on them - could have just been to use up missiles and generate revenue or to for a show of strength.
2. If I had grown up in some super strict religious society with very little access to educational tools/knowledge then I could have been one of those very same people that I, at the time, thought was "evil" or "an enemy."
3. You think that taking life is going to feel a certain way but you really never know until it happens and it changes as time goes by. I'm sure the experience is different for everyone and I'm pretty sure that if it had been up close and personal it would have been 10x as potent.

It doesn't keep me awake at nights like I bet a lot of the ground troops have to deal with (some don't though, it just depends on the person) and I don't know that I really regret it...

The fact that I felt so certain I was doing the right thing, and so righteous at inflicting destruction, is the most unsettling part for me, and that's a sensation I don't really feel like sharing with other people or being forced to talked about because someone asked so I just don't tell people my history anymore, not unless I know them well.