This prophecy is flat out wrong because it ignores the future impact of genetic engineering. The rise of genetic engineering is going to allow humans to solely give birth to geniuses. This will more than counteract this idiocracy effect.
But if somehow they manage to understand organic balance and go for a more heterogeneous composition of inteligences, than it might work out as intended.
I guess the best approach is to just reinforce and even boost the genes that are already there in the gene pool of the human being.
Lets get just one intelligence characteristic for instance that will be sort of harmless to boost in everyone: give us more memory..
Except for the fact that forgetting about some things can do wonders to our psychology and for a human being resisting through all the years it must to..
Maybe the suicide levels will rise, and people unable to function in society will also rise, creating the opposite effect.
The thing is, this is a really complex matter, and i hope that when we are ready to do this, we live in a more advanced society (morally and philosophically) than we do now, or else the consequences of people that are unable to understand the consequences of what they are doing, do it without being really prepared for it.
For me, the the nazi-germany of the 30's is a (extreme) cautionary tale of a possible future of ours, where we are technologically advanced, but morally corrupt, and that combination will probably lead to the human kind fallout, if nothing changes..
Our technological progress is good, but we need to rethink other important things, and the movie is on spot over this (they had all the technology to solve the problem, but they had the emotional IQ of toddlers).