It wouldn't make double spending easy, double spending is stopped at the receiving end, and if another transaction makes it into the blockchain before this one, that one is the valid transaction. I'm not suggesting this as a means of defrauding vendors, most won't ever accept transactions that they can't send directly to the network themselves. I need it, primarily, as a means of getting transactions to and from an old computer that is isolated from any network. It's really hard to hack into a computer without a network card, which makes a great place to put a savings account. Getting coins into it just involves updating the blockchain, which is easy enough to do. Getting coins back out of it is tricker.
I'm thinking that I'm not likely to be the only person that will come up with a use for transactions that can be saved to a file or piped.
Then I think what you really need is an "export" function, which has been requested several times in this forum.
Basically it would allow to export some bitcoins into some private keys in a wallet file. Of course there would be also an "import" function, for antagonist purspose.
That would be nice, but standard unix tools would fill this role easily, and much besides. The idea that security is enhanced by opposing the realase of common tools, on the assumption that they could be used fraudulently, is false. If they could be used in that manner, then the secuiryt model is already broken, and someone will be writing these tools for that specific purpose. I don't believe that command line tools of this nature will materially impact security of Bitcoin. If I'm wrong, please point out how, so that I may sell all my holding now and watch this whole thing fail.
