Each to their own but personally I'm not too fussy about a bit of dirt.
It's good for babies because it helps them to build up their immune system and it gives their immune system something to go to war with. It's possible that the current prevalence of allergies is partly caused by the fact that the immune system hasn't got enough germs to fight so it fights things that are harmless.
I sterilised Yasin's dummies for a while but once he started licking the floor I no longer bothered.
My SIL is a scientist and she did her PhD thesis about immune systems and she's pretty much got the same philosophy as me about germs.