This does two things. First, it makes it so that if someone feels strongly enough that they're right to be willing to risk the penalty, the public still gets the information. This is important. It's a check on the courts getting it wrong.
And the second is that in order to punish someone for speech, you have to prove it in court in a public adversarial proceeding where the person being punished has an opportunity to defend themselves and the claim is aired as part of the court record in a context where everybody knows that it's in dispute but the media and any interested party still gets to find out what it is.
This is obviously not what happens when you implement a general prohibition against all claims of election fraud with no meaningful opportunity for anyone to view the material being censored or make their case that it shouldn't be prior to its removal.
People are not defending fraudulent communication. They are observing that the same factors that make audiences vulnerable to misinformation affect the censors and the process by which censors determine which information is harmful.
If we had a test for truth or sincerity we could use it to determine which information was false or put forth in bad faith. We don't, so any person who acts as an information gatekeeper could be one of those people who is lying or deceived and they would then be able to corrupt the discourse by censoring the information that exposes their lies or misunderstandings.
There is no US law that would stop someone from making expressions that are later determined to be fraudulent.
Note, commercial speech (e.g., advertisement) is considered a less protected species of speech and may be subject to prior restraint in limited viewpoint neutral circumstances.
I'm pretty certain you're 100% allowed to do this, though Pepsi inc may sue for damages.
But no US law can prevent you from saying it in the first place.
neither does youtube removing videos.
But more importantly, I don't even think your charity example works. Like you can be charged with fraud if you just put the money into your bank account, but if you collect for a charity and charge a 75% collecting and handling fee? Are you then collecting to a charity?
In this case it is more that somebody claims you are not collecting for the charity, you show the bank statements that conclusively prove (according to yourself) that you were collecting to a charity. Then somebody starts looking into it and claims they have evidence that you play golf with the bank teller. And that their manager is your college buddy.
And now you try to suppress the (alleged) photos.
To be clear, I don't think there was widespread fraud or voter suppression in favor of Biden. But the key difference is that normally there are disinterested parties (in particular courts) that can rule on the evidence, in politics there are by definition no disinterested parties in the US. And because of the superpower status of the US, it is even worse outside it.
There's always been an expectation of truthfulness in communication: We don't allow people to go around claiming that Pepsi causes AIDS, or cures cancer. You're not allowed to claim you're collecting for a charity, and then keep all the money for yourself. I doubt you'd be terribly okay with me claiming that you're a murderer and asking how much that biases your stance.
(Genuinely trying to understand if there is something that makes this different from any other sort of fraudulent communication - I don't see people defending the other stuff under the guise of "Free Speech", and I'm not clear why this would be different)