In the 90s I was at a little internet startup, and the product guys _insisted_ that a verification loop for registered emails would be catastrophic and lead to a massive dive in registrations. Engineering pushed back, it went all the way to the CEO, and he sided with product. So we built the damn thing, and it went live, and the CEO got signed up for _everything_ we could think of. Wasn't more than a few days of this before verification suddenly became a good common-sense idea.