[zarastralia]

>Is it necessary to be unkind, even slightly?

No, sure, it isn't. However, one can write a useful reply in terms of content without being aware one is being unkind.

In such cases it will feel something like 'wow, I'm so clever today' or 'he deserves a good solid fisking'.

The trolls are useful in that they bring this problem into awareness. Kindness/decency is a requirement for continued discussion, which is at least as important as discussion itself.