So what happens when everyone adopts slightly incompatible variants of this system?
Endless loops of "Please pay me 2 cents via PayPal so I will read your message with the Subject: Please pay me 3 cents via PayPal"
Oh, you'll put in an exception for those messages?
Next message is from your mother. You're going to charge her 2 cents?
Ah, whitelists. Management problem.
Also: PayPal can't efficiently handle micropayments. (Well, for 33 cents apiece, they will.) So you need your own micropayment system. Which will be incompatible with your prospective customer's micropayment...
Endless loops of "Please pay me 2 cents via PayPal so I will read your message with the Subject: Please pay me 3 cents via PayPal"
Oh, you'll put in an exception for those messages?
Next message is from your mother. You're going to charge her 2 cents?
Ah, whitelists. Management problem.
Also: PayPal can't efficiently handle micropayments. (Well, for 33 cents apiece, they will.) So you need your own micropayment system. Which will be incompatible with your prospective customer's micropayment...