Yes, it is theft. There is no indication of the original creator/source, they make it seem as though it is their own content, and they are trying to profit from others work. You have YouTube channels, you know how little each view can pay, and you know how much a single upvote could get....don't you want that single upvote too and not for the person who posted your video to get it. You might get .00000001 for the YouTube view from YouTube and the person who posted your video might get a $10.00 upvote....Is that OK with you?