Online culture may have driven this, but in a survey of people in the USA people were asked which type of person they would least like their children to marry. The “types” were things like same-gender, transgender, Christian, Muslim, no-college, Republican.
Those who identified as Democrats had Republican as “least liked”.
Those who identified as Republican had the first two I listed.
However more polarised online is, that above is real world polarisation, and it’s pretty serious.