Personally I hate photographs with watermarks, they ruin them completely. If this site permitted photographs with watermarks it would greatly devalue it. I belong to some aviation sites as well, and they won't permit watermarks either.
Like it or not, if you post your photographs anywhere on the internet, there is a risk they will be "stolen" by someone else. I post knowing that is a possibility, it's up to everyone to make their own decision.
I totally agree.
I have seen my photos used on other sites eg brokers etc, but as this is just a hobby, I am not losing financially, although it would have been nice to have been asked permission.
Not posting photos at all because of this just means that some excellent photos will never be seen.