Free speech is the wrong framework for thinking about this. Tech companies are not government actors, so this is not a free speech issue. The better way to think about it is to analogize to gun sales. Gun sellers are within their rights to refuse to sell guns to people with nazi affiliations, etc. But they wisely choose not to go down that road, because if they did (1) they’d be enlisted into screening all sorts of other people (hate groups, abusive spouses, mentally ill people, etc.) and (2) when one of those people inevitably did buy a gun, there would be increased pressure to hold the gun seller/maker liable for failure to use their discretion to prevent to the tragedy.