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Date: Tue, 26 May 2015 19:10:25 +0000
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From: Gregory Maxwell <gmaxwell@gmail.com>
To: Tom Harding <tomh@thinlink.com>
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Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] First-Seen-Safe Replace-by-Fee
Precedence: list

On Tue, May 26, 2015 at 5:54 PM, Tom Harding <tomh@thinlink.com> wrote:
>  It's not difficult to
> imagine real-world consequences to not having contributed to the
> transaction.

I'm having a hard time. Can you help me understand a specific case
where this makes a difference.

It appears to be a gratuitous requirement;  if I have another unused
input that happens to be larger by the required fee-- why not just use
it?

The inherent malleability of signatures makes it unreliable to depend
on the signature content of a transaction until its good and buried,
regardless. And an inability to replace an input means you could not
RBF for additional fees without taking change in more cases; there
ought to be a benefit to that.