Hello!
I am not that active in the suggestions forum, especially not in the major discussions, so I haven't seen such behavior myself. However, I do agree with the OP that attacking newbies is not necessary.
The reasons why people may miss that something already exists can be manifold, actually:
* Failure to read they should check the forums (mentioned before)
* Inability to use the forum's search tool (probably rare, but possible)
* Looking for the wrong search term (probably not that rare); especially since they are newbies, they may not know the terms regularly used to refer to certain things, like HFS, for instance.
* Failure to understand the structure of the development homepages (concerning things already on the to-do list)
As I can see these possibilities for making a redundant thread without any actual malice on the part of the newbie, I do not think we can condemn them for making that 'mistake' right away.
Politely informing them about there already being an interesting discussion and pointing them to the relevant thread via a working link should probably not too much to ask for. Usually, when you do something like that, you will get some response showing how the newbie feels about it, and personally, I think that in most cases it will be gratitude and maybe a little bit of shame, together with good intention not to repeat the mistake. While I don't care for the shame bit, the intention to be more thorough with the future checks and the positive feelings the person obviously has towards the community are things I consider quite useful for the community. They increase the chances that a) the newbie will not repeat that 'mistake' while b) still being active and contributing to the community. And since the reasons for the initial behaviour can be manifold, that newbie may actually be a real source of inspiration for the community - if we only allow him/her to settle down here and share their views and imagination.
In addition, in such cases, the community should also strive for efficiency as was hinted before by other posters in this thread. Once the newbie has been informed about the existance of the other thread and provided the link, what else is there really to say about that case? I wouldn't be surprised if the "flaming" criticized is not actually the first response pointing out the redundancy, but rather other people chiming in adding nothing new except their disdain for the newbie. It may be just me, but such expressions of disdain do not seem like a useful contribution to the forums, so in effect, those additional posts are empty and a waste for the community at best.
In addition, such aggression may eventually leak into the general atmosphere as well, poisoning it. Especially in a diverse group like this (and this community is rather diverse due to the complexity and flexibility of DF which poses many interesting moral decisions to the player), a good atmosphere of tolerance is very important, I believe. If people start being elitist and exclusivist, it will in the end only tore the community apart, rendering it sterile as exclusion of the others replaces inspiring exchange of views and fostering creativity.
Well, at least that is the way I see this issue in general, having not faced this problem here myself.
Deathworks