It used to be that you can opt to not monetize so that no ads will be played. This move however means that even if you don't monetize and/or not opt to allow ads to run when people watch your stuff, YT will still be able to run ads (if they wanted to) when people watch your stuff. If you are not monetized (either you opt not to, or, not eligible), then ad revenue goes solely to YT and zero for you even though you could be getting a few cents, so why not? If you opt to monetize, then YT shares some with you.
Bottom line is, just opt in for monetization, if you are eligible. If you don't, then I'd say that's pretty "un-smart" of you, whatever your reasons may be. You don't get any sainthood points for not doing so. If people don't want to see ads, there's ad blocker and etc stuff people can do to go around it, so let them do that.