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As I explained, none of those reasons apply to PaymentRequests.
As they exist today PaymentRequests allow for essentially the same types of transactions as non-PaymentRequest based transactions with the limitation that OP_RETURN values must be greater. In that sense they're basically a pre-OP_RETURN environment. OP_RETURN serves a purpose and it can't be used with PaymentRequest transactions.
> I have no idea what you are trying to say here.
I think if you think through how you would create an OP_RETURN transaction today without this BIP you'll see you need a key at some point if you want a zero value.