DBS checks do very little to prevent abuse, mostly they are about liability. They are about the least important part of safeguarding.
Things like having changing areas in visible places, workers not alone with kids, etc, are more important.
Sitting next to one person on a bus rather than another may or may not reflect a bad sort of racism or sexism. Often, it has no real effect on the other passenger, so it's irrelevant. Though I remember a young black man in my high school history class talking about women crossing a street when passing him if there was no one else there, which he perceived as fear of black men in particular. Was he right? Maybe, maybe it was just fear of men generally, but it clearly did have an effect. Which isn't to say it was unreasonable of the street-crossers.
Discriminating in employment though, in giving people seats on planes, on pulling over their cars, based on statistical analysis of sex or race or religion, is at another level. Which is why we've drawn legal lines around those things, and need to have very strong grounds to justify going over those lines. Grounds that go beyond that aggregate set of numbers.