I've done it once- on an NYC travel forum, another member pretty well raked me other the coals in a discussion over paying respects at the WTC site. That poster pretty well lambasted me, accusing me of some rather unsavory motives, even dragging in what her mother might allegedly say, if she was there. (Just an aside- when you're arguing with me, I don't care what your mom/SO/Whoever would have to say if only they were here- they're not here, so leave them out of it, I'm only interested in your opinion)
It was obvious that nothing I could say was going to change that person's mind, or even convince them that I wasn't some attention seeking nutjob (just for wanting to offer respects in a manner appropriate to my faith), so finally I said it. "We're not going to agree on this. Think what you want about me, I'm done defending myself to you." True to my word, I didn't revisit that thread, I was truly done with it. I wasn't looking for attention or sympathy, I wasn't hoping anyone would beg me to stay. It was simply not productive to continue that argument, and I didn't need the increased blood pressure.