Even though the 1st amendment (or any amendment for that) has no bearing on HN, I agree with the spirit of your idea. I remember a month back, someone said something that I found funny (http://news.ycombinator.com/item?id=193369) ... and I put a LOL on it and I lost karma points for it. Seemed nuts to me.
I think downvoting on an "lol"-type comment is appropriate. Making that sort of comment adds nothing valuable to the conversation and actually detracts from the comments by adding unnecessary clutter. Whenever you want to "lol" a comment, just upvote it.
