The morality surrounding ad blocking is up for debate, but I do not feel guilty because there is no OBLIGATION for me to view ads. Just because you serve them up does not mean I need to view them. I don't view ads on TV, live or DVR'd. I don't look at roadside billboards or look at magazines because they contain too many ads.
I don't like being tracked, seen as a means of income by fly-by-night operations, a target for malware because the ad server operators are too lazy to secure their servers because there is no ROI in server security. In short, I have a right to protect my precious bandwidth and my computers whilst on the Web.