The Flynn Effect. People aren't getting more ignorant, we're becoming more aware of our ignorance. Of all the foolishness and idiocy in the world, if you look at human history it's always been worse than now.
With grade inflation and babysitting modern age students, what are the realistic requirements to attain a university degree in a low-difficulty major at a mediocre school? 80 IQ? 85?
The literacy argument is trivially refuted in a similar manner. Reading by itself is not indicative of higher cognitive function above an elementary school child.
Also, proportions are what matter here. I doubt the proportion of people with high fluid/crystallized intelligence is higher now, than it was, say in 1850. The only difference is that now a higher proportion of the general population have degrees.
I realize we're talking about humanity as a whole, but I don't see the appeal of the 70's.