Reddit mentions of Good Germs, Bad Germs: Health and Survival in a Bacterial World

There's book for that.

Beyond the obvious suggestion in your comment, there is actually a biological reason for this as well.

Keeping your environment too clean seems to cause the immune system to not react properly to innocent environmental input; i.e. t-cells overreact to certain innocuous environmental stimuli and cause higher rates of allergic reactions. Chronic infection at a young age causes lots of problems throughout life and isn't helpful, but regular exposure to environmental agents, dirt, germs, etc - things which aren't infectious - appears to train the immune system how to react properly.

Kids who grow up on farms and in houses with pets tend to have lower rates of auto-immune disorders than kids in very clean houses - and wealthier families in my experience do seem to tend to have more sterilized homes.

Check out the great book good germs/bad germs for more info (and good info on anti-bacterial resistance as well).

You know i just started reading Good Germs, Bad Germs: Health and Survival in a Bacterial World, bout 1/2 way through.