This is why for serious things we have notaries. People forge signatures all the time. With a digital signature, you lose a lot of the forensic information (handwriting style, etc) that would aid in proving that you in fact signed something, but I digress.

If I write a script that goes to every web page on the internet and fills in all text fields with "jdJdkjl28d", selects a random choice from all drop-downs, checks all check boxes, and hits submit, no one is going to seriously argue that I would be bound by any of those agreements because I didn't read them, and the logic I wrote isn't even aware that they are agreements -- it is just checking checkboxes regardless of what the form says.

This is why some companies make you scroll all the way down to "read" the agreement before you can check the box because then it can be argued that you actually read the agreement.