A signature is somewhat harder to take them and checking a checkbox and can be somewhat more easily traced back to the signatory, so it’s probably somewhat better than a checkbox.
You're free to counter and say it's a forgery just as you would be to counter and say someone stole your private key. But the point of a signature in particular is that it's supposed to signal considered intent rather than mindlessly checking a box or being rushed and saying "sure sure whatever."
We pop up dialogs to ask users for confirmation before doing dangerous actions. What's wrong with the paper equivalent?
* TOS - a simple checkbox - or even just a "continue button" * Moderately large purchase - type your name * Larger purchase - draw your name * Major contract - use this widely recognized signature flow
You'd need to perform the DSA algorithm in your head on the content of the contract, using your memorized private key, and write out the resulting signature block.