I started vaping near the beginning of 2010 without a particular goal beyond smoking less for all the various reasons one might want to. Unlike many here, I wasn't an instant quitter. In fact, I haven't stopped smoking. I don't intend to. (On the other hand, I don't particularly intend NOT to quit either.) I enjoy smoking, and have for well over forty years. BUT, I have been very consistent in the past year and a half in keeping it down to no more than four cigarettes every day (down from 20-30). Besides enjoyment, I figure my routine of barely smoking/mostly vaping gives me some sort of equilibrium: Had I chosen to give up smoking entirely and then got tired of or annoyed with vaping, I'd probably have gone back to smoking at my old rate very quickly. Plus, by still enjoying those few cigarettes, I exempt myself from becoming one of those sour anti-smoking types I so dislike. And I figure the four or fewer cigarettes I still smoke every day are not doing much to me, as compared to the several hundred thousand I smoked in the years before.
Your mileage may vary, but I think whether one uses e-cigarettes to quit smoking, to cut down on smoking, or, for that matter, just to supplement smoking at times and places when one can't, it's not my business to tell them they should feel bad about it.