It is true that people who watermark get more comments from other photographers expressing a dislike of watermarks than do photographers who don't use them. It is not true that watermarks are useless in the digital age, and it is not true that the decision not to watermark an image never offends.
1) The first reason why I watermark images is because every lawyer I've ever had has advised me to do so. While it's true that watermarking an image does not prevent theft (people can crop it off or photoshop it out), if someone posts an image of mine without my permission in a way that omits the watermark, it displays an intent to steal. It shows they wanted it to be seen as their work and not just an appreciation for my work. All new photographers should be familiar with their rights as laid out in the DMCA Section 1202.
2) Some of the clients I have worked with have asked me to watermark my images of them that I post on the web because their lawyers told them that it's best to have watermarked images out there for similar reasons as I stated above. As a portrait photographer, not only do I have to be concerned about people stealing my image, but also my client's face. Someone taking my client's face and using it on a site that promotes child abuse or molestation would not be good for my client. And yet again, while my watermark does not prevent them from taking it, they are removing copyright identifying information, which is illegal and could win us a law suit.
3) To my knowledge, nobody has ever stolen one of my watermarked images. I also have never noticed anyone cloning it out or even cropping it off. It's just much easier to steal a similar image from someone who doesn't watermark. When I park my vehicle, I lock it because if someone is going to steal, it's easier to take the one that is left unlocked.
4) I give complimentary tear sheets to models. I'm sure they get a lot of them. While every photographer would like to think the model remembers which photographer took every shot, watermarking them ensures it never gets mixed up. It then frees up the model to post it where ever they desire to post it without typing my name everywhere or answering a thousand people wanting to know who took the photo. It also avoids other photographers of accusing the model of a failure to credit me for my photography. Similarly, I often give complimentary tear sheets to gallery owners, art show organizers, museums, or interested clients, and it is much easier to habitually watermark every image to ensure they have my information for later. (And yes of course I also use business cards.)
5) Honest to God I have had people referred to my site because they saw my information on a watermark.
You will notice additionally that my watermarks do not run through the middle of my image, and very rarely are they ever opaque. There are certain times when I will take that extra step, but ordinarily I use a faded watermark in one of the corners. I also advise new photographers to use Digimarc and fill out the necessary fields in their EXIF data.