I have bipolar II. I think the biggest risk is that manic episodes cause temporarily impaired judgement and increased risk-taking. This can lead to people saying things they genuinely believe but would normally keep to themselves. Or, people might pick up and repeat things during manic episodes because their judgement is impaired.

If we're talking about Kanye West: Kanye was diagnosed with bipolar in 2016, but made comments about Jewish people and power as early as 2013. I think he was thinking about these ideas either early on, or before he started showing symptoms. Untreated manic episodes might have made it worse.

I appreciate your question was asked in good faith. I want to be very careful in emphasising: bipolar people are not going to become nazis. This is one very specific case. It's possible, but it just doesn't seem to happen. This is an uncomfortable time for people with bipolar, as one person's actions are contributing to the public perception of all of us.