"One of the sad things about Internet discussion"

I don't consider that to be a "sad" thing at all. Of course it can be misused (sockpuppets) but it can also allow people to speak out who may be reluctant to do so under their real name.
The internet is about choice, use your real name or use a handle, the choice is yours.

I've been considering doing the same, given that various anonymouos email correpondents have been making predictions about my future health.

That can be unpleasant Peter. However it's been my experience that the sort of vermin making those threats would wet themselves with fear if they met you face to face.

What's treacherous about sock-puppetry is that a poster can us screen-name X to pretend to be a decent human being and at the same time use Screen Name Y to show his true persona - that's the dishonesty. If a poster cannot be straight and honest about what they really think , then I don't think either Identity should be here. There are a couple of people using SNs here whose views I dislike intensely, but fair play to them they don't dick about being nice to my face with one Screen name and post trash under another name.