other than it was a campaign promise?

Lets say you have two individuals. One works in a fast food place. The other serves in a sit down place and receives tips. They both make the same amount of money. One makes theirs through wages. The other through tips and a small wage. But the totals are the same.

So why should one have to pay tax on the entire amount they make and the other only on part?

In what kind of world can this be right?