I don't think this is true. For pretty much everyone except either small business owners or the very wealthy with exotic assets, the government already gets all

I don't think this is true. For pretty much everyone except either small business owners or the very wealthy with exotic assets, the government already gets all the forms it needs to calculate all your taxes (employers send W-2s, brokerages already send 1099s, your bank sends your mortgage statement to calculate things like mortgage interest deductions, etc.). There's no reason it can't be automated for 9 out of 10 people.