The truth is that relative income is not directly related to happiness. Nonpartisan social-survey data clearly show that the big driver of happiness is earned success: a person's belief that he has created value in his life or the life of others.
There is nothing inherently fair about equalizing incomes. If the government penalizes you for working harder than somebody else, that is unfair. If you save your money but retire with the same pension as a free-spending neighbor, that is also unfair.
The more control you have over your life, the more responsible you feel for your own success - or failure.
We will have bigger bureaucracies, bigger labor unions, and bigger state-run corporations. It will be harder to be an entrepreneur because of punitive taxes and regulations. The rewards of success will be expropriated for the sake of attaining greater income equality.
If you think spreading money around by force seems like an odd definition of fairness, you're not alone.