NOTE: I am not saying that anyone else is wrong in taking their pups out earlier or anything. In fact, apparently there are reputable sources that back this philosophy up. I am just saying that I personally do not feel comfortable doing that.
If you are going to take them out early, it should be thoroughly researched on how to go about it, so that you reduce the risk of them getting sick.
I think it is a great idea to socialize your pup, but I think there are multiple ways to go about it.