It's a loss of the trust of your users. It's ever harsher data protection laws. It's the vehement reaction you get when you say to someone, "your personal space is mine for the taking, and maybe I'll take a little less of it if you beg me to stop." It's the slippery slope of dark patterns to cajole and conceal and browbeat users into avoiding the opt-out. It's the camel that starts with its nose and then quickly removes you from your own tent. It's the grab first, apologize later modern world of capitalistic exploitation all in the name of gaming the quarterly numbers. It's the next paving stone on the road to your users crying out "We're mad as hell and we aren't going to take it anymore!"

Lol... always amusing when someone asks HNers what changes they'd like to see and why, and they respond with crazy analogies that are totally unactionable... not the first time this has happened, won't be the last.

As others have pointed out, change opt-out to opt-in. Don't send a single byte until opt-in is complete.

Change your frame of mind from "my software" to "your computer". If your users don't explicitly opt in, you have no right to take what they do not freely offer.