So one might endorse a substantial comment which is incorrect just so one can downvote it for being wrong.

And that is where this solution falls down. You are relying on a subset of people to ignore their human nature and endorse things they do not agree with.

Whilst I'll admit they maybe some who will do this, I believe the majority will just follow their instincts. This sort of behaviour can be seen in any internet forum.

Inevitably new posters are required to write posts they think will be endorsed in order to achieve the karma threshold needed to use the site properly

Can you find a different term for it? To 'endorse' something means that you support it, and that you put your name behind that support. The action you're describing is more like 'publish' or 'pass' or 'authorise'. Probably 'release' is a good term, given the concept of 'pending'.