Well, it's a joke because the problem becomes apparent after you think a bit about it. The exact same reasonig can be applied to anything illegal, criminals are criminals because they don't respect the law, so you could try to say that laws are useless. Reality is, if something is illegal not only someone can be punished after the fact, but in some cases also preventive measures can be taken.
Regarding the comment, it isn't going to stop anyone. Most people will not do cybercrime because they're honest. Of the remaining, the risk of being sentenced to jail time will instead stop some people, even if not all of them.
As you're basically saying, the world isn't black or white. There's also a category of people that needs an incentive to behave. Also, without any laws, it would be problematic to punish "the bad guys". At that point, what you can or cannot do would be only a matter of relative power: who is stronger can do whatever they want to weaker people.
Nope, it reduces the issue even if it isn't solving it entirely. Without laws and law enforcement, anyone with bigger muscles than you could break your nose just because they feel you looked at them the wrong way.
So? Anyone with a badge can wreck your life with zero consequences, even if they're a pipsqueak. Many of these individuals absolutely hate being looked at the wrong way.
Physical violence is just about the last area we "need" laws because people really hate violence and will go well out of their way to avoid even the chance being subject to it. No matter how big you are you can't go around breaking noses without a good reason we all agree on because if you do that for very long a bunch of other people will gang up and break yours or worse.
To a first order, laws basically just codify how the government (the overwhelmingly dominant applicator of violence in any given society these days) will apply violence so that the peasants can reason about it in advance and avoid it.
You don't need any of that for the basic "if I do violence upon others without a damn good reason violence will be done upon me" workflow though.
I think you are forgetting that laws are responsible for a good chunk of what people perceive/are educated to see as good/wrong honest/dishonest.
Sure the worst atrocities are known to be bad from Religion (10 commandments, which is a law in itself) but many aren't. Speeding, drunk driving, harassment aren't concept that are obviously wrong (as in obvious to people with no guardrails).
So laws aren't useless. The fact that most people respect them actually means they have a purpose.
Regarding the comment, it isn't going to stop anyone. Most people will not do cybercrime because they're honest. Of the remaining, the risk of being sentenced to jail time will instead stop some people, even if not all of them.