I think your comment typifies the tribalism and faction-based shaming that OP was alluding to.

Telling Republicans “there is no legitimate reason to vote Republican anymore” is not a logical argument that will win people over.

I could not disagree with you more. The Republican party is not a far-right extremist party, the Republican party is an extremely confused and poorly defined cooperative between conservatives and liberals. The Democratic party, on the other hand, is increasingly radicalizing and unifying in favor of socialized policies.

I think that the American left wing is far more unified and further left as a collective than the heavily fragmented and incoherent right wing. American liberals have effectively been excommunicated from the left wing, and as such are beginning to represent a sort of tentative alliance with the conservatives in opposition to the Democratic party.

TL;DR, I think the Democratic party is more cohesive and further left than the highly polarized Republican party is right.

It really isn't. Mainstream Democrats like Pelosi and Schumer actively work against the more radical Democrats (sabotaging Bernie in the last primary) and are into big business and banking nearly as much as Republicans are. That's why the Democratic Socialists of America exist -- right now as a group within the Democratic Party, but conceivably as their own party in the future.

Putting aside the fact that Bernie isn't a democrat...

Most of those in government (just to make abundantly clear I mean both parties here) are there because they want power and money, not because they have principles.

He ran in the Democratic primary, so he was in that election.

Only when it was convenient to say he was. He's never been a democrat.