I think the argument is that open source is based on the fundamental ideal of trust - I put this software out into the world so that people can better it, tweak it, make it their own. If those people don't trust you, and have to audit everything they install, the model breaks.

Re binary blobs - honestly, for me at least, if I'm installing a blob it's probably because I purchased the software. Maybe it's naive but I more or less assume no company is going to actively screw over a paying customer