Also, I think we should all realize that bothsidesism in the United States, whether it comes from the left, right, or disaffected center, exclusively benefits the Republican Party. Republican voters who can't defend Republican policy use the "both parties are the same, so who cares" throw away justification, just as some on the left do to excuse voting third party or not voting at all.
In reality, at least for the time being, the American left coalition needs to act like right wingers in terms of electoral strategy. Right wingers never use bothsidesist arguments to impugn the Republican Party or to excuse not voting. Even when they are critical of Republicans being sell outs, globalists, n*****-lovers, etc., they maintain perspective on the party being definitively preferable to the Democrats. And that's why the far-right is winning: Republican figures are more afraid of their primary threats than of Democratic challengers, yet no matter what the whole right turns out to vote in the general. That's what the left needs to do: put Democrats into power and, if they cross us, pour money and attention into primarying them.