Why not watermark? I do, for a few reasons:
For the record, I’m not completely against watermarks, just against watermarks that deface the image. I don’t use watermarks but my photos usually have embedded EXIF data. Yes, you can remove that easily too, but it doesn’t show and anyone who cannot remove a watermark probably won’t bother with EXIF data either, at least not knowingly. Unfortunately Facebook removes EXIF data from everything you post there, which is a reason my Facebook page has nothing on it, and also a reason for adding a discreet watermark.
The benefit of watermarks has been seen. I found a photo in another photographer’s book, which had a watermark and traced back to the owner. I don’t know if she took any action or let it go. On the other hand, I looked at other photos in that author’s books and traced them back to various stock sites even though they did not have watermarks. I still don’t know why a photographer would write books on photography and use someone else’s photos, but that’s a separate issue. I think the major benefit of watermarks is advertising, if your photo is spread around the Internet. That can be achieved even if you put a fairly discreet watermark in a corner, or down the side. It doesn’t have to be at 100% opacity and square in the middle to be a benefit.