has to do with peoples motivation.
Let's say you pay tax, because everyone pays tax, because you think the money goes to a worthy cause.
However, if someone else does not pay, you decide not to pay, because otherwise it seems "unfair" to you.
That means, that at the end of the day, the worthy cause was less important to you, than the fact that everyone should suffer equally.
If the cause was more important, you would pay regardless. So some peoples
