That was more true in the 60's, and so we never spent the time to try bringing this to production. We don't need to make all of our nuclear reactors capable of producing weapons-grade material anymore, and I don't think there's much objection to new reactor types on those grounds.
Actually it was never true, but it makes a good story. Sorensen in particular claims the fast reactor program was favored because of its weapons applications. Nothing could be further from the truth. Fast reactors, from their conception, were pursued for sustainability reasons by pacifists like Zinn. The first electricity ever produced from fission was produced by EPR I. Every single gram of fissile in the world's nuclear weapons was made in a thermal reactor or enriched from ore. The MSR program was cancelled along with myriad other programs during the early-70's recession... including the nuclear rocket programs, the Apollo program, etc.
There has never been an economic case for the breeder simply because the fuel cycle is such a small part of the cost of nuclear energy. When you have a factor of 5,000,000 you can afford to throw away a factor of 100.