Well, you can also forge a regular signature. In proper legal contexts, you need a witness to a signature (which is a justice-of-peace or similarly trusted party in Australia) who will check your identification and witness you signing the document. Signatures are more of a ceremonial thing at this point, they just are used to signify that at the time you agree with a document. If you dispute the validity of a signature, it becomes a forensic investigation (which would also apply for electronic signatures I imagine -- ignoring that digital forensics is such a bad science).

Scanned copies of passports are also seen as sufficient ID in some contexts (though they should be notarised copies, very few online services require that). And that's even worse becase the person getting the copy could just impersonate you with it.

I would keep in mind that most disputes are not of the "I never signed this" variety.

Even companies like DocuSign acknowledge that fact: "DocuSign electronic signatures have never been successfully repudiated or challenged in any court."