J.J.. you say "Do enemies make us stronger and more accountable? Sure, but why do we need Republicans in particular?"
My answer is that at the moment, they're the only viable opposition party around. The GOP presidential candidate got 74,216,154 votes in 2020, 46.9% of all the presidential votes cast. In the 2020 House races, the GOP got 47.7% of the votes cast, up 2.9% from the previous election and the Senate is split 50-50. You could wait until you're old and gray before the GOP disappears.
Though you and I might agree about the danger to democracy that recent GOP behavior represents, apparently, almost half of America believes the lies and propaganda spewed by Fox. Speaker Pelosi needs to show America that the Democratic Party is not the band of leftist radicals that Fox and the GOP have painted them and is eminently qualified to govern. A scorched-earth legislative program by Pelosi is unlikely to achieve that end.
I know you believe that the polls you quoted show most Americans back things like Medicare for All. I would caution you that unbiased polling is almost impossible to execute and that the votes cast in the last election seem to contradict your conclusion. We both agree that America has grave and pressing problems to solve. I fear that increasing our political polarization is unlikely to help in solving them.