Is it morally right to persuade someone to vote Labour if they're voting Ukip?

To be fair, these people aren't very bright and could be thought of as typical 'Kippers anyway, and all a Ukip vote is gonna do in our constituency is bring down the Tory majority slightly.

So should I persuade them to vote Labour even though it will have no effect since we live in a Tory safe seat? Or should I just let nature take its course?

[Also as a 'side' question (since it seems preferred I don't start too many threads a day), do you like it when people say 'there's more to you than what meets the eye.' I take it as a compliment and an unintended insult. Unintended insult because it suggests that what meets that person's eye is a person incapable of achieving great things.]