I think the only bad things might be
a) boredom

b) too many strange ideas in your mind
c) the cost...although books are generally cheap
Right now I'm having a "break" from reading popular science but am working on a new wish list so my next Amazon order is not too far away...
Seriously, though, I think that reading lots of popular science books teaches you lots of things. You learn to be critical and you start to wonder about the writer's credibility. Where did they find this fact? Didn't I just read something else in another book? Then you start seeing contradictions in the texts and you realize that you are starting to actually know something about things.
So my reply would be no, read as much as you can, but as with everything else make sure you take a break and read something else...like crime. Or sci-fi. Or watch a movie!
Tormod