I don't deny that many avatars are 'stolen', but that fact is not a valid argument against their use
What is required here are sustainable arguments for the introduction of avatars.
The figures I quoted above, while an unscientific sample, suggest the following:
* Around two-thirds of members will not bother to upload an avatar, meaning that around two-thirds of posts will feature a generic "Saddo" icon, and while I don't doubt that the intention is to enhance a sense of community and cheer up the look of the forum, in my experience the effect is the exact opposite - all those generic "Saddos" in a thread look like nothing so much as a row of tombstones.
* Many of those who do upload an image will infringe copyright (few newbies read the rules) and in some cases will probably "steal" the image from another member's website (sparks will surely fly).
* Some text slogans will be used (something like "God Hates Fags" is very legible at 50x50 pixels).
* Almost nobody will upload a genuine photo of themselves - the stated reason for the opening post in a thread that has seemed badly mistitled ("Allow Picture in Profile") from the start.
* Moderators will have plenty of extra unpaid work to do.
As before, assuming viewing is optional I don't have any personal objection, but I don't have to write the policy and deal with the problems.
The positive benefits are that many members like them
Many members may also like animated gifs, rollovers and Flash (though probably not BLINK tags).
demolishing paper tigers is a sacred duty for those who see them for what they are
If you can formulate a coherent policy that addresses all the potential issues you might get somewhere.