Earlier quoted context omitted.
The law isn’t like programming. The reason you sign something is to show clear intent that you intended to agree to something. Nobody’s under the impression a paper signature cannot be forged either. It’s no different. It’s social not mathematical.
Then that leads to my second question >Why do we need them at all? Why not just email the contract, and the person replies back with "I agree to this"? Simpler and cheaper than paying $150/year.
The best way to see signatures, in my IANAL opinion, is as layers of protection. The goal is that the person who signs the agreement has total understanding of what they are signing, and there is a paper trail of intent to abide by the agreement.
To that degree, if the agreement is important and you have a lot on the line if the counterparty decides to re-neg on the agreement, you should probably not do the above. But going in the opposite direction and insisting on notaries and wet ink might go too far in respect to how much effort is required.