I'm not sure people are afraid, maybe they just don't want to be belittled. I know personally that I've thought twice about posting my crappy newby photos because of the people on forums who just insult rather than help. But I've actually been really lucky that everyone has been lovely and welcoming, and have provided kind criticism.
I think there's definitely a way to word critiques, and that maybe you don't always word it in the best way, whether that's unintentional or not.
I'm new here and have had a good mooch around the threads. From what I've read I can see that bonsai is your passion - you love it and do want teach your ways to help people improve their trees. Which is think is great, but I do think it's important to consider that the people behind the usernames and photos are human beings with feelings. I'm a teacher, and even though I teach children not adults, I believe that people do not learn through negativity.
Reading through this thread has made me feel relieved that you haven't come across (or wanted to comment on) any of my photos. I'm sure you could offer some really useful info and things to work on, but I'm not sure it's worth the hammering you'd probably give me.
I hope I'm wrong though, because I think this is a brilliant resource and community and I hope to stick around for a long time