Ugh!
This comment conveys the all-too-common reality that "cultural fit" is code for "everyone should be like us." To the extent that cultural fit is a defensible hiring criterion, or even a good one, it doesn't mean pure homogeneity.
There are a lot of ways where it's obvious that you don't want homogeneity. Take the question above. It may be good for the company if all of the individual contributors like being taken advantage of, as they'll work long hours for bad pay or whatever. But if your upper management or sales team likes being taken advantage of, they're going to let the company be taken advantage of, and now it's not so good.
In a lot of things, it's way healthier to have a mix. You want people who like and excel at starting projects and laying good groundwork, and you want others who like refining and maintaining systems that are already defined, because any company that's still building new systems will need people to do both. In most development teams, having all of either will be bad news.
And the same goes for personality issues. It may seem great to build a culture around people coming in at the same abnormal time as you and liking the same kind of fun as you. We're all together all day! We can bond through that fun! But there are a lot of problems that crop up as you grow. Once your culture is defined by, say, being a bunch of 23-year-old men who come in at noon and love video games and drinking, people who don't fit some or all of those characteristics might not feel especially welcome. Hiring people for areas other than engineering gets hard. Hiring senior engineers who are more likely to need to be home by 6 gets hard. Hiring women gets hard. You've just boxed yourself into a pretty small corner of your potential talent pool.
I've seen great companies built out of beautiful mixes of people. A married foodie who lives in SF working alongside a through-and-through Southerner who thinks In-N-Out is exotic. Fresh out of college video game players alongside parents with two decades of experience who like hiking. People still got along great and had a lot of fun together. There were certainly some commonalities, but I'm sure people would answer personality questions in drastically different ways. That doesn't mean they don't "fit" together.
There certainly are some cases where rejecting someone on "fit" reasons makes sense. Say you interview someone who is technically great, seems to be able to generally work well with others, but is terrible at pair programming. Will never cede the keyboard or listen much to their partner, and doesn't seem to be trying to fix it. If your company does a lot of pair programming, don't hire them. If you're a company that doesn't really do pairing, this might be a bit of a red flag, but it's not a deal breaker. There might be some analogs in the personality space.
But culture fit definitely should not mean "we have identical personalities."
This stuff matters. I'm the kind of person who would pass a lot of "culture fit" homogeneity tests (young, white, male, pretty nerdy, elite university), but I hate the homogenous cultures that often crop up at Valley companies and actively avoid them. A major factor in choosing to intern at Matasano this summer instead of some companies that are filled with very happy 22-year-old men is the much more reasonable culture, and all 'tptacek has written on HN about how "culture fit" is often BS.
So if you build a culture where "fit" means "be like us," you won't just cut out a lot of people who aren't like you, you'll cut out people who are like you but prefer communities of diverse people.