I just realized that, unless your comments are very related to an article, they can be very damaging to your keyword density. I wonder what the effect is in Google.
dont worry too much about kw density. comments will only help, even if it dilutes some density. those days of 17% or 21% kw density for higher ranking is long gone. these days, 2% kw density is good enough given that you have the proper onpage elements and quality backlinks