In fairness, that's not the argument. What Superman's saying, to a degree, is it's about trust and respect. If Superman suddenly started tearing up buildings and threatening people, he's Superman. He doesn't do that stuff (anymore). It's really easy for the public to accept "okay, yeah, Starro." Because he's Superman and he always takes the least lethal approach.
The Ultramarine Corps., on the other hand, had pretty much built themselves off the premise of "We will totally blow up your city if that's what it took to beat the badguy." So they have much more of a credibility problem when they say "oh, we got mind-controlled."