I have also noticed how some very experienced posters jump straight to harsh criticism when someone is asking advice or sharing an experience. It seems to be a lot of the same posters too that will pick on everything and never have anything but criticism to share. It's a shame because I think it scares people away, newbies and not-so-newbies, and hinders this great learning environment. I am trying not to let this dishearten me or prevent me from asking my "stupid" questions, because I can also see that there are a lot of tolerant, humble and helpful divers in the forum too, and so far I have received some great advice from them.
I have been diving for 5 years now, and still consider myself a newbie. In the past 2 years I have spent a lot more time in dive shops hanging around dive professionals, and I can see there are some big egos out there. I have often wondered if scuba somehow attracts people like this, but then I have decided no, I think it is more of a natural psychological reaction to sharing the same interest with so many people which sparks feelings of competitiveness and also insecurity (at the realization that they are not as unique as they thought they were). Someone who has dedicated a lot of time and energy to become something, and places a lot of weight on their identity as this or that profession, will naturally feel a little bit threatened by others who are doing or have done the same as them. I have seen this with professionals, academics, and even travellers. Take a look at the lonely planet forum, it is full of big egos that are always trying to one up other traveller's experiences and rip into posters who dare comment about something that don't know as much as he/she does about a certain topic.
As far as diving goes, I see it more with dive professionals working in the industry, rather than just experienced recreational divers. I have experienced a lot of cliquey snobbery towards less experienced divers in the diving community. If you are just a student recreational diver, they are more than happy to help, but then once you start talking about taking your diving to the pro level, some divers seem to give the attitude. In many ways I think it is a territorial thing. Let's face it, there are a lot of people out there that want to work in the dive industry, but there is a limited amount of jobs, and it is very easy to get certified to become a dive professional. I think it ticks some of the more experienced professionals off that they are considered in the same league professionally, and have to possibly compete for jobs with people who are not as experienced as themselves. I can understand this because I have experienced something similar myself. Years ago, I studied to be a yoga teacher. After taking my personal practice very seriously for many years, I went away to an ashram and spent months training to be a teacher. Afterwards, I came to my hometown and the most recent yoga craze hit and brought all kinds of new teachers onto the scene. Nothing wrong with a little bit of healthy competition, however, I was bothered when I found out that all the new teachers in my area had been certified by a weekend course offered by a travelling van! It was hard to stay humble and to not feel a sense of superiority and criticism towards the others, and I did my best to contain my ego (like a good yogi!). Now that I am older and have given up teaching, I feel a bit silly for feeling threatened by other people who were pursuing the same goals as me, but I also know that this is a natural reaction for normal human beings. It happens to people pursuing anything, professions, hobbies, academics. We need to prove our worthiness, and sometimes for some people, that translates into criticizing the expertise, opinions, or experiences of others so that we can keep ourselves on our pedestals.
Also, we have to keep in mind that people say things online that they would word differently in person. It is so easy to be snarky on a forum because you can maintain distance and (to a certain point) anonymity. I also think it is worth pointing out that sometimes words come out wrong in writing. Without facial expressions, tones of voice, body language, etc. to accompany our words, sometimes they can come across as harsh even if they were meant to come across as something else, like concern, for example, as Jax said.
We all have our stories to share, and we all have the right to express our opinions, whether harsh or gentle, that is what these forums are for. My advice to newbies is not to take it personally, and just to remind yourself when people are being harsh with you, it is either out of concern or ego. If its concern, feel grateful for them, if it is ego, feel sorry for them.
for a moment. You may be a newer diver but you seem to have great experience with internet forum communication as seen by your explanation here 
