Defamation is more damaging to the average nobody than it ever could have been 50 years ago. If anything the laws should be strengthened.
I could hypothetically accuse you of being a rapist right now. I can just pick a random day I say it happened, let's say last February 23rd. Cool, it took me about 30 seconds to come up with that. Let's say I then blast that all over Twitter and Facebook. Are you okay with having no legal recourse? Are you okay with "jrockway is a rapist" being one of the top Google results for your name? Maybe it's better, maybe you did really well and your rebuttal is the first Google result. I would still be really uncomfortable that my first Google result is me attempting to say that I'm not a rapist.
That's assuming people will even read your defense. There are some classes of accusations where you will be tried in the court of public opinion before you are even aware, and your attempts at defense will only be interpreted as further evidence that you are guilty. The rise of Fake News accusations should tell you exactly how much telling the truth is going to help your case.
Rape is a particularly heinous thing to accuse someone of, but I chose it specifically because of the "believe the victim's narrative" messaging that surrounds it. Accusations of a crime fall under defamation laws, and so long as they don't file a police report about it, defamation is the only law I'm aware of that it would violate.
(Unlike more pressing issues facing society, this one doesn't require spending money, or passing a Constitutional amendment, so it feels within reach!)