Well, I do think it’s rather strange that leftists are orgasming over the idea of a slightly more anti-white version of George W. Bush getting elected.
The conservative base at least managed to defeat the GOP establishment and put up a candidate, flawed and obnoxious though he may be, who represents their interests.
A few things might be clouding the issue. for one thing, "leftist" has a lot of different possible interpretations, and it seems among conservatives it is "anybody less conservative than Barry Goldwater". Biden is basically a centrist. I think by design, he has basically sat at the midpoint of the Democratic party on just about every issue, no matter how the party has changed. If you are a goo-goo type who thinks the system basically works, with the possible nedd for a few reforms on corporate power and maybe some slight improvements to the socia safety net, Biden is great.
He is better than great, because Trump is a huge thumb in the eye to that philosophy. Trump represents a break down of the facade of liberal idealism, that the world is post-racial and post-political, and all that is left to do is work out the fine details of exactly how neo-liberalism should be implemented. Trump reveals an America deeply riven by racial paranoia and economic inequality, and the ease with which our constitutional and legal structures can be undermined if people decide to ignore the norms of the system. (This was true before Trump. The rise of the religious right and the Gingrich coalition and later McConnell's grinding congress to a halt under Obama made that clear to those with eyes to see. Trump just made it undeniable.)
If you are little more to the left, in the AOC,/Sanders wing of the Democratic party, getting rid of Trump is still great news. His policies are immoral and his influence on the country is baleful. But a Biden win is a decidedly mixed blessing, and strengthens elements within the party that support a deeply immoral status quo on issues like economic inequality, racial discrimination, police violence, etc.
It you are even further to the left, (it me), you are happy Trump is gone, wish someone who would do more good things than Biden had won (I was partial to Sanders or Warren), but ultimately don't believe any president is going to be able to fix what is wrong with the US or the wider world, and that it will take a deep restructuring of social relations to do so.
So the first set are delighted, everybody else is just relieved Trump is gone but are dissatisfied with Biden. The folks in the second group will continue to try to drive the Democrats left, and the actual Leftists will continue to organize outside of government.
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