This person sees various diversity programs, policies, or actions that specifically help women and people of color and think one or both of these things: (a) this isn’t fair to them, or (b) this “lowers the bar”
If one doesn’t see the unique challenges that women and people of color face, then the existence of programs to support the advancement of these people appears to be unfair. Many men don't see the challenges women and POC face every day, but they do see the very visible programs that attempt to remedy these obstacles. Programs, policies, and practices attempt to make an unfair playing field level. It’s also true that for some people who feel unconsciously entitled, that equality feels demeaning to them.
It can also be useful to confirm that what they’re describing does happen to some degree: at some point somebody probably was chosen because of their race or gender who was not as experienced or qualified as white or male candidates. But it’s not representative of the norm. This scenario could not possibly be representative of what normally happens, otherwise corporate leadership would be overwhelmingly female and POC, and it’s quite the opposite. Hundreds of studies show that women and POC are most often disadvantaged in ways that aren’t as visible.
While confirming that what they’re saying must happen at times – and perhaps they can name an egregious example of it – you can ask them what they make of the different studies and statistics that the many ways they’re hugely disadvantaged in ways that are less visible.One study from the University of Toronto showed that even companies that include pro-diversity language in their job ads discriminated against POC applicants – and sometimes worse, because these candidates were lulled into a false sense of security and did not take steps to “whiten” their applications by making their names sound whiter or removing professional and personal achievements related to race (source).