So you're saying if my dog goes out in the back yard and eats critter poop and then comes in and licks the kid in the face he's going to be healthy?
Well, how's your kid? (I mean, aside from maybe bad breath?)
Some germs are generally to be avoided. That's usually why the things associated with them stink.
But one of the healthiest people I have known runs a 'honey dipper truck', cleaning out septic systems. He's probably been exposed to more pathogens than most humans, but never seems to get sick.
I think the run of the mill germs in small amounts give the immune system something to work on, like exercise, that keeps it at the ready to deal with other stuff, too. Maybe my reasoning is flawed, but we exercise muscles so we can lift the heavy stuff--if we don't, we can't. Seems like the immune system would work much the same.