US government expenditure is more than $6.3 trillion. The $3.6 trillion you quoted is just federal spending, and does not include state and local spending:

http://www.usgovernmentspending.com/total

So, it's more like 50-something percent, not 100%. Also, some of the money would come back as sales tax etc., so the real impact would be less than 50%.

At the height of the great depression only ~23% of workers were out of jobs. That's hardly 100% during a "downturn." At 100% unemployment do you really think our current system of privately owned property would fare any better? Personally I think at 100% unemployment the masses would seize all the property, and probably rightfully so.

So are you inserting a qualification for being unemployed and no longer allowing just anybody to walk in and demand their share of basic income?

Then you're back to the problem of needing to hire more bureaucracy with respective office leases, equipment, etc., to verify the employment status.

Unemployment is also a weak estimate, what you want is unemployment + the negative labor force participation - kids and retirees are not unemployed in the sense that they're actively seeking employment, but would probably not pass up an opportunity for free cash.

BI is typically given to everyone as a basic right - including those with jobs.

>That's $300 billion a month, $36 trillion a year

Math error here.

Thanks, corrected.