I don't think you can ever avoid the two factions from taking pot shots at one another because the two have such differing views with the others being sceptical of those views.
Some pros think anyone with a DSLR attempting wedding photography is trying to 'cheapen their art' 'steel their livelyhoods' 'earn a quick buck' etc etc and in a way fair play - However, every business no matter which sector it is in always has to compete with other people undercutting to try and break into a market with inexperience and using substandard equipment - so deal with it!!!!
I don't think it's so much that, as it's a matter of professional "pride" and standards.
Someone posted a thread on here the other day saying that their photography hobby has spoiled taking snapshots for them. They wanted some simple snapshots of the kids coming off the ride as Disneyland, and they found themselves no longer looking at the smiles on their kids faces, but at composition and oh, no, there was something in the background that spoiled the frame. I would imagine that the majority of wedding pros seeing a bad photo of a wedding are similarly compelled - I'll bet they can't help themselves from groaning with frustration.
I would wager that the majority of wedding togs here - those with years of experience - hold themselves to very high standards. I'm self-employed in an unrelated business, and fortunately it's a job that I can often take my time over - if I do it wrong, I can just do it again, and get it right, and only charge my customer the time that it took for the second attempt. Wedding togs don't have that luxury, but I'm sure many of those here are equally self-critical as I am.
I've also been in the situation where someone comes to me because some other guy mucked the job up. I work with computers, and I've had people come to me because some other guy formatted their hard-drive and they've lost years' worth of photos of their kids, or messed up in countless other ways. I will bet you 100-to-1 that a number of the wedding pros here have met brides who have been in tears over the wedding photos that some other tog has ****ed up.
When I think about my fellow unprofessional "professionals", and consider how a wedding is a once-ina-lifetime event that you don't get any second chances to photograph, I can really see why, in any case of doubt, a wedding tog would advise "just don't do it".
On the other hand, I have seen threads on here from people, who clearly have not thought about what equipment they need to do a wedding or thought past the fact they are going to shoot a wedding at all!!!! That for me shows a real disrespect for the couple and people experienced or not, who are actually putting time and effort into their photography.
People entering the market (and I class myself in that bracket) are all adults, who should be responsible enough to know when they feel right and competent enough to begin their wedding photography career / part time job / way of funding upgrades to their equipment etc etc and are probably charging rates that reflect this
I think that it's not "the threat" (as you say) of competition that causes the seasoned pros to discourage the over-enthusiastic amateur. Some people just don't have the competence to judge their own (lack of) abilities. The old saying is that "incompetence tends to rise to its own level", but in the wedding photography business there's very little check upon this. Whereas in regular employment one has a boss who can say "well, he's not ready for that job yet" or "he messed that up, so no promotion", wedding photography is all undertaken by self-employed individuals, and they can get any job that they bluff.
There's a wedding photographer on here who takes bookings (presumably paid) yet who posts in their portfolio photographs with background clutter coming out of the heads of the subjects. I don't think that one should even be claiming to be a decent or competent amateur if one is making that mistake - it would only take a step or two to one side, to reposition the subject slightly, and the photos would be much improved by the standards of many readers of this forum. And these poor shots are in the photographer's portfolio - presumably these are their best images, the ones the togger is most proud of! I hate to imagine the standard of the rest of their shots!
In the cases that the bride & groom get to see the portfolio of the photographer in advance, well, fair enough. They know what they're getting. And it really highlights the fact that the public don't have our sophisticated appreciation of the art of photography - the bride sees her wedding photos and it brings to mind her happy memories of the day, so it must be "a good photo". That's fine - the important thing is that she's happy.
But I can really see where the pros are coming from, because I'm absolutely sure that all the experienced wedding togs here will have dealt with the aftermath of a wedding tog who has oversold himself or misled the happy couple, with tears as the result.
Stroller.
PS: the reason these threads keep coming up is part of the culture of the forum. Someone posts a thread here titled "lens advice" and no-one tells them "the subject of your post should indicate Canon or Nikon (or whatever) and approximate focal length" or "this question was asked last week - use the search function". People make posts asking "which of these two lenses should I buy" without stating what they plan to use it for, or even their general photography interests. "Which first SLR?" is asked on a daily basis, and newcomers are never told "well, what did the last thread say, then?" (even though the most common reply is always "try it for yourself"). This is a very friendly & accommodating forum, but it does have its downside - a newcomer to the forum can come here and make such equipment advice posts with giving it a thought. They receive useful advice and do not then know any better than to make another post about weddings.
sometimes you've just got to know when to say 'No' haven't you
but hey, I've only electrocuted myself twice I say to no avail 
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(I loves you too mate!)
