I think echo chambers are part of the problem. Previously you'd love in your village and have to get along with other villagers (or move, which took a lot of effort) so people had to learn to compromise more.

Now everyone can live in virtual echo chambers where everyone agrees with them and they never need to compromise. So they start viewing anyone who disagrees with them as pure evil.

"Every biologist knows that small groups in isolation evolve fastest."

Small groups that are isolated aren’t necessarily echo chambers devoid of diversity. The point is the existence of disconnect between small groups, not the homogeneity within groups.

Can any biologist reading this confirm or deny this statement?

Broadly true. It's standard stuff. Think about Charles Darwin and his writing about the unusual diversity of the species on the Galapagos islands, which are small and isolated. There are numerous other examples, e.g. pygmy species on Mediterranean islands (now extinct).

When population numbers within a species are large, interbreeding will tend to dilute genetic mutations within the total population. When populations are small, e.g. due to physical isolation or temporal isolation, mutations are more likely to spread and become established. This is increased further when selective pressure is applied.