Really it's just the inversion of Pascal's wager.

Very few people will inherently desire to follow the doctrine of whatever religion they happen to be; because of their beliefs, they choose to do things that they otherwise wouldn't.

Homosexuals, for instance, might submerge their sexuality; this will likely serve to decrease their overall happiness. A Catholic couple in Africa might catch AIDS because the church tells them condoms are evil. An impoverished woman might elect to carry a foetus to term, condemning herself to poverty and creating a person who grows up in circumstances that nobody deserves. One country might view another country as inherently evil by choice; these two countries might even welcome nuclear war as a fulfilment of divine prophecy. Somebody with multiple sclerosis might vote against stem-cell research because they think zygotes have souls.

Perhaps most frightening of all, humanity might never explore space because the universe is only there so that our planet Earth can exist.

All that's just off the top of my head. I'm sure there are even more dire threats that theism might blind one in acknowledging.