The rules aren't the same for everyone anyway. There are numerous deductions that have a much higher impact on how much or little a person pays than marriage. Deductions in taxes are given when people believe that those things that are given deductions are seen as benefits in other ways to society.
Plus, this doesn't really stand up well in an argument for abolishing marriage, only tax incentives for marriage. If you think these are wrong, convince others that they are so they work to change those laws. Otherwise, you are simply complaining. And it sounds like you are trying to throw the tub out with the dirty water when there is no reason to do so.