What does "grated even on proponents of the deal. " mean?

Context>>>>>>>>>>>>>>>>>>>>>>>>>
In retrospect, the helipad was probably a bad idea.
The proposed transportation hub for senior Amazon executives was supposed to sit atop one of the company’s gleaming new skyscrapers along the East River, part of its planned second headquarters in Queens, New York. But the image of Amazon Chief Executive Officer Jeff Bezos and his well-heeled lieutenants bypassing the city’s congested subway system grated even on proponents of the deal. It also handed political opponents a convenient catch phrase—“Stay the helipad out!”