You don’t need to have experienced racism to understand this you just need to have been a spectator vs participant. Having grown up in an extended family in which child abuse was absent, it was no more than a concept to me. When I was in a relationship with someone who had been abused, it wasn’t until I witnessed a conversation between her and her parents that I suddenly realised I’d listened to her stories but didn’t fully believe them. It wasn’t because I didn’t trust her it was because it didn’t fit my experience.
You can live with an intellectual understanding of something you can’t relate to so long as you don’t have to confront the dissonance. You can sympathise with a sufferer and even fight their corner and yet doubt their experience. This is why people experience the fatigue – the cognitive dissonance.