> why is there such outrage about taxing option and RSU income?

There is no outrage, or even opposition to taxing income from selling options and RSUs.

The problem arises because in some situations options and RSUs are considered "income" as themselves, not a potential to make income when they are sold.

You get some options in an early-stage startup, and have to pay tax on that. But you can't actually sell your options - there is no market, and often you aren't even allowed to sell them before the company is acquired or goes public. There is still a good chance that the company will go bust before either of these happens.

So you have to pay a tax bill years before you actually earn income, and potentially without ever earning income from your options.