Why? Why can't the leftists push people down rabbit holes and make them rabid communists? Serious question.
One utilitarian-- it's a smaller market.
E.g., there was story on the intercept sourcing leaked FBI documents that showed the FBI's awareness and concerns about white supremacist infiltration of local law enforcement[1]. This was to the point that the FBI was cautious about sharing access to its surveillance tools for fear that they could be used by some local LE to target and harass minorities. (Not sure if that's in the same article or a different Intercept article.)
Racist rabbitholes can draw on a pre-existing audience of racists, which make them more widespread and effective, and that attracts more ad dollars.
Two-- emphasis on "rabid." There are racist groups where the membership is people from various ethnic backgrounds spouting the stereotypical white-supremacist rhetoric. The draw is apparently aggression and violence.
If someone on the left wants to "counter" that, the video content is going to need to be equally irrational and aggressive to sufficiently capture the audience's attention. Again, you've got a smaller audience here. But the smaller audience you gain is going to be equally irrational to the far right group.
So you've got a system that optimizes for irrational, rabbit-hole ideologies (hell, it could be bigfoot or flat earth for all they care), that tends to filter out more reasoned, thoughtful content. Hell, I can't even listen to a movement of a Brahms symphony without commercials interrupting a section. Even television isn't that fucking allergic to reasoned reflection.
Talking about free speech inside such an unhealthy, anti-democratic system is about as coherent as adopting one of that system's rabid, rabbit-hole ideologies.
1: https://theintercept.com/2020/09/29/police-white-supremacist...
And with this specific case, I'm with you on your hill.
But more broadly we're usually not talking about the web from the late 90s. We're talking about a handful of modern social networks most of which use of anti-democratic dark patterns. And algorithms that are known to push a given percentage of users down a rabbithole, who can then be weaponized for who knows what purpose by who knows which nasty actors.
In essence, we're talking about factories which-- if there were a market for it-- could produce a version of the internet from the 90s with the slight difference that a sizable proportion of your 90s internet acquaintances happen to spout racist rhetoric and becoming walking, talking bioweapons this time around.
I know that's not the topic here. But that is a much bigger problem IMO and the answer of "more speech" is at most helplessly incomplete wrt it.