I'm not quite sure I understand your analogy because I think most would agree that knives should not be regulated and we shouldn't investigate and punish knife sellers/makers for stabbings.

To play along with your analogy: if social media sites are well-designed, they do what they're supposed to do: communicate information or misinformation. And just like how we don't crack down on knives even though there are plenty of stabbings, we shouldn't be cracking down on social media & online speech even though there are plenty of liars and idiots who spread misinformation.