what tax system do you propose that has no audits or enforcement?
Uh, as far as individuals go, how about the one that was working pretty well before 1913...
If you think the first U. S. income tax was 1913, take a peek at this 1864 income tax form and instructions - THAT was our first income tax.
http://www.salestax.org/library/1863form24.html
The 1913 income tax (form and instructions here):
http://www.salestax.org/library/1913form1040.html
was actually our THIRD income tax. The second was a corporate income tax in 1909 ... but you'll have to did out the forms yourself.