Absolutely, a 30-30 will kill them just fine. I would bet there are thousands of elk killed every year with 30-30s. You will have to be within 150-ish yds and place your shots well, but a 30-30 will work fine. After all, they were wiped out in most of the eastern states by settlers with 36 to 45 cal black powder rifles, and a 30-30 has more energy than those do.
Never try to educate someone who resists knowledge at all costs.
But what do I know?