"Visual Effects Artists, if you measure by the number of man-hours worked, are a relatively small portion of the labor that goes into a movie, even one like Avatar or Titanic."
A movie like Transformers or Avatar can have hundreds to just under a thousand people working on the VFX for anywhere from 6 months to year (for the main portion- R&D will occur during and before principle photography).
More people will work on the VFX side will appear onscreen, or during principle photography.
Don't believe me? It's the best example (and one you cited) but take a look at the Avatar imdb page:
http://www.imdb.com/title/tt0499549/fullcredits#cast
Probably over a thousand people on that full cast and crew list, and the VFX division starts at 20-25% down and continues until you're 85% down the page- and that's not taking into account that the post production processes (especially on a movie like Avatar) go on for much longer than principle photography.
So, more people for more time equals more man hours- thats the mathematical point of the argument, but it wasn't the point I was trying to make.
The point I was trying to make is that no one went to see Shia Lebouf in Transformers or Zoe Saldana in Avatar- they went to see the Visual Effects- and in this day and age that's becoming pretty common.
I am not trying to argue that VFX workers are more important than grips, teamsters, actors, DPs or Directors; all I'm trying to say is that when Hollywood begins to rely on VFX for it's blockbusters, VFX workers deserve the same deal everyone else in the business is getting- wage guarantees, contract abuse protection, healthcare, residuals that pay into benefits, etc.
Take a look at the worldwide box office list,
http://boxofficemojo.com/alltime/world/
and ask yourself how many of those movies relied heavily on VFX. As far as I can see, in the top 10 only 2, Titanic and Dark Knight, aren't "VFX Movies" but they still had incredibly amounts of VFX work in them- every movie made today (even romantic comedies) will usually have hundreds of shots that go into VFX (if for nothing more than zit fixes).
I actually posted my comment because I agree with you about video game developers needing a union.
As for people being against it, there are plenty- movie producers will scream bloody murder when the movement gets stronger; other unions will be worried that their benefits will be eroded (a Visual Effects credit cannot currently come before a 1st Unit Director credit; which is usually in the credit roll- I think VFX supervisor deserves an intro credit right there along with Director of Photography), and some VFX workers themselves are strongly against it.
It's a long hard road, and because of pressure from China and ease of entry into the industry, it might not make it.