It's an interesting paper, but unfortunately it misses the point. Polar dissimilar political beliefs are not the problem. Many countries have this, and even have lively political discussions that remain civil, rallies that remain civil, and elections that remain civil. The actual problem is psychological, specifically dealing with identity beliefs. Once a person takes on a belief as part of their identity, any attack…
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7462781/
As I understand it (I am far from deeply knowledgeable about the literature! I'm just reading a book on this right now), Porter and Wood's 2017 study was one of the first that called into question the strength or existence of the backfire effect:
Wood and Porter. "The elusive backfire effect: mass attitudes' steadfast factual adherence." Political Behavior, Jan 6 2018. https://dx.doi.org/10.2139/ssrn.2819073