His point is valid. If you rely on something that causes people harm that must be factored in when they seek to minimize their risk.
I don't use ad blockers because I generally support your position. I do block flash because it is so annoying and especially noisy ads and downloading video I didn't ask for on my limited bandwidth.
It seems to me it isn't 100% either way. There is an issue of being a free-riding meanie when you block ads those providing content rely on for income. There is also an issue of sites being overly obnoxious in their serving of ads. The users right to control their computer makes sense.
The risk of privacy violations and serving malware are real and impact the ability to claim blocking ads is fair.
Those that believe in blocking ads mainly don't believe it is ok for some ISP or others to replace website ads with their own ads. This is normally based on the idea they don't have the right to change web content clients request and this argument largely relies on the same idea those that say ad blockers are wrong rely on. It is true there is space between these arguments to slip in the claim that while others don't have the right to eliminate the web content and replace it with their own the end user does. This is a reasonable argument, but it is not, IMO, without a reasonable counter-argument (that those providing the web content are doing so with the ads as part of their offer).
I don't think ad blockers are immoral or unethical but I do think they are not 100% pure either. They are a reasonable thing to resort to given an understanding of the whole situation. But they do, it seems to me, take away an earned benefit from those providing content.