Case in point: I recently edited this picture: http://en.wikipedia.org/wiki/File:Turing_Machine_in_Golly.pn...
It's a screenshot of the 6 octillionth generation of a Turing Machine built in Conway's Game of Life, using the GPL'd program Golly. The previous image contained Windows GUI elements (title bar, etc) which are non-free and cannot be used on WP when a free alternative exists. So I cropped it and uploaded the edited image.
Within minutes, I had received a template on my (seldom-visited) commons talk page informing me that I had uploaded a file without specifying its license, and that it would be deleted. Take a look at the "Permission" field on that image: "See LICENSE.TXT distributed with Golly for GPLv2 license"
Despite this (incredibly clear) assertion that the image was GPL'd, I received a warning that it would be deleted. Why? Because I hadn't included the "This image covered by the GPL" template that a) I didn't know existed, b) there was no mention of on the upload page, and c) is a wordier version of what I wrote in the license field.
As an experienced editor, I'm used to these stupid quibbles and time-wasting fights. I'll still contribute, although they are a large part of why I don't contribute more. As a new editor seeing this, however? I would have told them to fuck off, got banned for incivility, and never gone back.
There's an attitude among the regulars that Wikipedia is a treasured resource that must be defended against innumerable vandals, trolls, and spammers by a select cadre of noble volunteers. To an extent, they're right. But when you have such badges as "The Defender of the Wiki Barnstar" [1] being held up as the height of achievement for veteran editors, it engenders a culture that is exclusionary, if not actively hostile, towards new editors.
[1] http://en.wikipedia.org/wiki/File:WikiDefender_Barnstar.png