Imagine Person A works a job that pays $100k annually, while Person B has no job and earns nothing.

Before taxes, everything is evenly balanced. Person A expends $100k worth of energy, and receives $100k in exchange. Their gain/loss is zero. Person B also breaks even, since they did $0 worth of work and were compensated appropriately with $0.

A: $100k (cash earnings) - $100k (work) = $0
B: $0 (cash earnings) - $0 (work) = $0

Just like how buying a car for $50k and selling it the same day for $50k should be considered a gain/loss of $0, the same must be true in regards to selling your labor for the same price that you paid for it (with your time/life-force/knowledge/effort).

But if we take $20k away from Person A through taxation, they now incur a $20k loss every year, because in spite of doing $100k worth of work, they only retain possession of $80k. It would be equally absurd to demand $20k from Person B, but because of a logistical technicality (namely that it's easier to rob from Person A's cash balance than to physically force Person B into unpaid labor), Person B is left alone and ends up better off.

A: $100k (cash earnings) - $100k (work) - $20k (taxes) = -$20k
B: $0 (cash earnings) - $0 (work) - $0 (taxes) = $0k

That's before factoring in welfare, for which only B could possibly qualify.