This is my own personal observations, and my opinion only... my apologies if I end up way off base and off track...
Some do come off with excellent advice, but the method of delivery may or may not be very good, others come off with horrible advice with excellent delivery, others just want to preach, while yet others are on a personal mission to prove everyone else wrong. I personally try to always look at the message which is being delivered and not the delivery, understand the context of the message, and the spirit in which it is being posted. There are subjective matters with some posts that we may not know or never know, for instance, they are posting because they wanted to help, but had just a few seconds, or posting from a mobile device that typing more then just a few sentences is an excruciating process, or it is a very raw issue for the person because they just suffered through something similar.
The point is we can not be face to face with the respondent and are not always aware of the full context or situation surrounding their response.
I know for instance, my response here for some is going to result in a TL;DR by some, possibly infuriate others, and possibly get completely torn apart.
There are some in every community be it on here or anywhere else in the world where there are the over zealous and everything in the world has to be this way or that exactly or else the world is going to end. There are those too that choose to ignore suggestions and things work out well, or often enough disastrous.
You give a couple of great examples, but this is the way I see some of them which may be different then how everyone else on this or any other part of the universe may see them.
For instance the breeding. If someone is doing the breeding for the right reasons, there is a very good chance they are going to read a large part of the breeding forum before ever posting a question about it, at least that is what I would do, then ask for clarification on some of the things which may have conflicting information in it, or may not be clear to them. From what I've seen these people also seem to ask their questions in a more constructive way, get a lot less resistance if any at all, and receive extremely helpful targeted answers, the reason why is because they've done their home work before hand.
There are those though that feel there is an easier, softer way of learning which is to just post something to the effect of, hey I got two beardies and I'm gonna breed them, give me the cliff notes on how to do it. Then when resistance is met they snap off with they are telling you not to do it so they can make more money selling their own. I have seen posters that in just a few weeks time went from being in school living with their parents to being married and having a large colony of beardies, own a house with a successful breeding program. By the sounds of it they have camp fires going all night and they sing the beardie equivalent of kum by ya telling people to just do it, don't listen to those that are giving you warnings, basically saying it just works.
Your other example of the lighting question getting responses about the sand that is the viv. I look at this way, it's really no different than someone saying hey I just had a baby, and built a nursery, do you think this mobile which I hung over head is going to be pleasing and calming to the baby. Then someone notices the crib has lead paint chips all over it. A potentially dangerous situation that may not be directly related to the question at hand, but an important issue that should be brought to the attention of the person asking the question about the mobile. I have seen in the past when something bad happens such as a potentially dangerous sub straight has been used, and the results are disastrous, the person who has the disaster on their hands often say that they wish they had known better.
There are quite a few other "hot button" issues where people are divided. The beauty of beardeddragon.org is that regardless of your opinion, experience, knowledge levels, your thoughts, and ideas can be heard with everyone else's.
I am also sorry to say, but how the question is asked, and the language used in a question very often is also a factor in the kind of responses which are received. I've personally have noticed that posts which used a lot of l33t/shorthand/t9/txt speak, or contain a lot of errors, gets responded to very differently than those that contain very little or none of it at all.
I try to always keep in mind the old saying, a smart man learns from his mistakes, a wise man learns from the mistakes of others.