There's no meaningful slippery slope here either; because the vast majority of cases don't involve anything questionably true, they clearly involve statements that have evidence or do not, and where there's doubt, the protections are generally fairly solid (this is in the news often enough too; witness how Musk's knowingly false and clearly negative "pedo guy" comment was still not ruled defamation).
What's worse is the fact that you don't need to win a defamation lawsuit to punish someone if you're much wealthier than the defendant, because too many jurisdictions let each side pay their own legal costs - such that those wanting to stifle dissent can often simply threaten legal action, even knowing full well they'd lose. The point doesn't need to be to win, the point can simply be to impose costs that are felt unevenly.