If the garment is nothing more than a symbolic representation of the covenants, designed by earthly folks a few hundred years ago WHY MUST THEY BE WORN?
Well it depends who you ask. To me the reason is that we who have gone to the temple promised to do so in order to be regularly reminded of the covenants we made in the temple.
Why can't folks come up with their own symbols that may actually be meaningful?
Who said they can't? Go for it. by the way, your statement seems to imply that wearing the garment as a religious symbol is not meaningful. It certainly is meaningful to those who choose to view it as such.
While I no longer wear them, no matter hard I tried, (and I tried REALLY HARD), they just NEVER ever felt even remotely Godly, divine, holy, peaceful, comfortable, or anything else positive.
I do not think they were ever meant to feel godly or divine but rather to call our mind to remembrance. But you had a problem with them. Ok. Don't wear them. This does not meant others do not have a totally meaningful experience in relation to what they represent. And by the way, I find them very comfortable to wear. Better then briefs or boxers.
I wore them as a sacrifice, showing my obedience. But they were destroying my life, my marriage, my sense of being, my sanity.
Oh come now. How were they destroying your life and marriage. Don't you think there were other things at play here?
There are many ways to bring symbolism into one's life without such a thing.
For you perhaps but not for others.
I'm glad you guys have found a way to have them be meaningful but I think you are very much the exception.
I think you are most certainly wrong about this. My guess is most of the active TBMs that were them are quite fine with it and many find them meaningful.