From my perspective, someone evading tax, is like someone directly stealing from my wallet.
If someone doesn't pay his taxes, then I will have to pay more to compensate.
There is also a negative feedback cycle with people not paying taxes. If the neighbour doesn't pay his taxes, then I will not be motivated to pay my taxes, etc. So it's better to break this circle early.
The problem of underpaid couriers should be solved at the root with the delivery companies and work-force laws.
The whole tipping culture is a big question itself and one of the leading cause for extremely low wages. In comparison, the quality of service is extraordinary in Japan and the waiters are clearly driven by other values than Tipping Money as God.