Dogs and Dogs

My husband brought up a point that concerns me. I've always allowed my dog to get close to other dogs when I walk him... and even sniff noses and the such. Also, I like to take him to Pet Smart and/or Pet Co and he sniffs around and meets other dogs. I believe it is important for his socialization and well being to allow him to do these things.

My husband says that our dog could pick up diseases and such from other dogs from doing any of the above. Does anyone know of any of problems?

Donna