You don't need to get it exactly right, and you can actually set it to the point which you underpay a little bit and have to pay at tax time.Unless changes are made or life events happen mid-year...it would be very hard to get it exactly right.
Doesn't really matter to me if it was easy - taking a man's earnings is wrong, period. There's nothing preventing those taxes from going up and up and up.....and the fella actually earning them has zero recourse, other than taking a cash job.
Whether or not taxes are withheld from paycheck has absolutely nothing to do with whether or not taxes go up, and up, and up. Taking a cash job and not paying taxes, however, is illegal and you can go to jail for that or pay fines if you are caught.
Really far too much grief to worry about such a minor thing in today's environment are real issues.
And by the way, it ain't going to change in your or my lifetime.