Yes, you can get contamination at any point during the growing process with fungi and that contamination can be in the form of an untold range of different molds, yeasts and bacteria, some of which can be pathogenic. But there are mold spores everywhere in the air, bacteria and yeast too, so that's not a reason not to grow them.
I think you are misunderstanding what I was saying. Yes, indoor cultivation is no problem, growing in a bedroom or basement, no issue at all. But that is very different to what madmaster420 was saying, that his friend had mushrooms growing out of his basement walls. It's like saying that because you can grow cannabis indoors, then you could expect them to start growing out of the walls spontaneously. Ridiculous.