John,
A third party is not terrible, although it complicates elections, which again is not terrible.
It introduces uncertainty and anxiety. Biden has fashioned his 2024 candidacy on NOT Trump, and a third candidate in the general election undermines that.
For the reasons you write, the danger is that it may offer a path for Donald Trump to return to the White House, which America and the world cannot allow.
As previously discussed, Joe Biden is flawed and vulnerable; a third-party candidate exacerbates this and opens another avoidable risk.
Two excellent people, Dick Gephardt, and William Cohen, are outspoken about the danger.
Who becomes the No Labels candidate is critical. Joe Manchin could take more Republican votes and Larry Hogan more Democratic.
Many thanks. Best.