1. "It's a private company, they can deplatform whoever they want!"
This is obviously true to an extent, but as all communication is increasingly dominated by a few private companies, leads to a situation where free speech is effectively stifled not by the government but by an oligarchy. This is especially true since internet infrastructure like DNS is implemented by private companies.
2. "It's freedom of speech, not freedom of consequences of speech!"
Clearly this argument is absurd and wrong, yet I've seen it get touted nonetheless, notably in an XKCD comic. If the government threw you in jail for political speech, and defined that as "allowing free speech but simply having consequences of that speech", most would agree that's not true free speech. Yet people accept that flawed logic in other contexts.
If you can lose your livelihood for a political opinion, you don't really have free speech, yet that's increasingly the precedent set by Silicon Valley as a reasonable consequence of unpopular political opinions.
3. "We can't be tolerant of intolerant opinions!"
Again, perhaps some truth here in the most extreme cases, yet increasingly we label all but the most anondyne opinions as intolerant. The range of acceptable opinions gets narrower every day, and the consequences for diverging from it increasingly harsh.
To me it's an objective reality that there's a massive attack on free speech in 2020, especially in places like Silicon Valley and primarily by people who identify as "the left", usually using the fallacious arguments noted above.