http://research.swtch.com/generic
They do believe it's a useful feature, they just don't think the tradeoffs justify it yet. (People who loudly clamor for generics tend to ignore these tradeoffs.)
With generics, it's easy to end up in a situation where just by instantiating some simple-seeming class, you get a whole giant pile of stuff, more than any sane programmer would create by hand.
(I wish I had it at hand, but there was an excellent post from a .NET/CLR guy a while back that went into all the crazy stuff that got instantiated just by creating one specialization of List<T>, the associated performance overheads, and the things the compiler and runtime tried to do to avoid those.)
Go devs made it clear that Go won't get Generics, and it's fine.