Those people are wrong, and there isn't room: tax revenues has been roughly constant across enormously varying [1] rates. An increase in rates will scare marginal workers (people near retirement, moonlighters, the lower-earning member of a couple) off the labor market, and direct more efforts into reclassifying consumption as a business expense, canceling much of the increase in revenues, while leaving significant economic waste in its wake.

[1] https://en.wikipedia.org/wiki/Hauser%27s_law