http://www.vhemt.org/

what do you guys think?

Urgh, yeah I've come across them before. I'm against them, in essence. Firstly, I don't even think the courses of action they recommend would even have any effect ("voluntarily phasing out reproduction"). I mean, in principle it's possible for everyone to just stop reproducing, but this seems intuitively unlikely. A better course of action to pursue for them or anyone interested in causing human extinction would be increasing x-risks in some way.
Also, it's predicated on biosphere survival being a good thing, I've made it clear in the past that I don't really think wild animals have very good lives, so the biosphere surviving is not, in and of itself, a good thing.
Sooooo, yeah, I don't think the mission they advocate is a good thing and I don't think their methods would even help them to achieve their goals.

futile

I've read something about a city destroying itself that way. Still, it seems pretty implausible.

Are they planning on having everyone who joins the movement not have kids, or just get enough of a majority to get forced sterilization? The former is pretty much doomed. The latter is only nigh impossible.

I think focusing on things like using nuclear power would do more to help the environment than trying to convince everyone to stop having kids. Also, regardless of whether or not animals' lives are worth living, we will eventually be capable of making them more worth living, and we might actually do it. It would be far easier, if still very difficult, to convince people to do that than to convince them to stop having kids.