You seem to be arguing that a benefit of cash is that it facilitates ‘tax evasion’ because the tax man already gets more than enough.
For me the issue of tax evasion and whether or not the tax man already gets more than enough rather depends upon:
1. what kind of tax evasion are we talking about? And, 2. Who 's paying (or not paying) the tax?
If we talking about large scale tax evasion by wealthy people then I definitely don't think that the tax man is already getting more than enough from them and that those guilty of it should be severely punished, far more so than they currently are!
But if we're talking about somebody on a low wage either getting something a little cheap on the black market now and then or doing the odd cash-in-hand job once I a while then I don't feel that strongly about their 'crime' and, I'm sure, would often thoroughly sympathise with their tax evasion if I knew the full circumstances.
Many people not only pay their taxes but they pay them with pride. They pay them with pride because they believe the lie. If the lie was the truth then paying your taxes would indeed be something to be proud of. But it's not. It's a lie.
Some people realise it's a lie and resent paying their taxes but continue to pay them because they fear punishment or have no other choice.
Some people realise the lie, consider the taxman to be a thief and take opportunities to avoid paying tax. Those who do that run the risk of getting caught and punished. Funny (not actually funny) thing is, when the wealthy get caught evading huge sums of money, they don't get severely punished, but when the poor get caught fiddling a small amount, they get fucked.
Of course, if the lie was the truth then everybody should most definitely pay and all of those, each and every one, who didn't should be criticised. But it' IS a lie. The taxman IS a thief - a thief who promises much but delivers little (just have a little think about the cuts and the closures and the failing state of so many of our public services, utilities and infrastructure...) We should look after each other, not look after the thief, or believe the thief when he tells us he'll look after us.
The thief and the wealthy, btw, they're really well connected, you know, like really good mates or partners...
Edit: To preempt the almost inevitable comments from predictable posters I will admit now that I am pretty much always amongst the second group of people I describe. Occasionally I'm one of the other kind.