I think argument is a good thing, both because it's a way of learning and because genealogy as a field of study has a long way to go.
So in my book it's fine to disagree, but it's also important to do it right. We don't have do be right, but we do have to play fair.
I can think of four simple rules for disagreeing without being disagreeable. Actually they're really just one rule plus commentaries. Please feel free to make additions or suggestions in the comments.
(1) Focus on the subject at hand, not the personalities. Don't say "You're crude and ignorant." Say, "I don't agree with [quote the offending matter]," and explain why. (Note that rhetorical tricks do not disguise personal attacks. It's little if any better to say, "Your statements are crude and ignorant," or "I think your statements are crude and ignorant." The point is not to draw filmy veil over our personal animus -- the point is to leave it aside and focus on the subject at hand.)
(2) Don't break rule #1 just because the other guy did.
(3) If you're not sure whether you're following rule #1 -- and even if you are -- ask yourself how you would feel if the other person said to you what you're about to say to them. Then don't do it. (Sometimes it helps to try turning your brilliant riposte into a series of inoffensive questions. Sometimes it helps to recall the last time you went ahead and said it, and how you felt the morning after. Ergo, sometimes it helps to just sleep on it.)
(4) When you do screw up anyway, back down and apologize. We all get to do this too.
I don't think there's anything snobbish or elitist or dishonest about these rules. (Do you? Why?). Nor do I think they're biased in favor of the status quo and doing things the way we've always done them. (Heck, I'm often not in favor of doing things the way we've always done them!) They're just a way for us to stick to the subject instead of getting into an actual fight -- because actual fights settle nothing.
No doubt one reason genealogists tend to be allergic to public argument is that these days most public arguments are abusive and don't follow these ground rules. Check out the comments section on almost any public (nonprofessional, nongenealogical) web site and see how long it takes the participants to start calling names.
Genealogists are already doing better than that. In a good argument everybody benefits.
Harper's Weekly, v. 3, no. 156 (1859 Dec. 24), p. 832; digital image, Library of Congress Prints and Photographs Online Catalog (http://www.loc.gov/pictures/item/2002735886/).
Harold Henderson, "Is genealogy ready for argument?," Midwestern Microhistory: A Genealogy Blog, posted 16 August 2013 (http://midwesternmicrohistory.blogspot.com : viewed [date]). [Please feel free to link to the specific post if you prefer.]