That's an interesting way to combat certain kinds of attacks - those in which the screenshot 'reveals' embarrassing, illicit, or illegal communication: things you've done or intend to do that have no external evidence aside from the message itself.

But it does not combat attacks that are not embarrassing but rather a release of information you are known to have but which is intended to be kept secret, or which is easily verified: if someone captures your social security number, private key, or home address in a screenshot, you'd better be really good at bluffing.