I definitely don't see anything wrong with people as individuals trying to influence how people vote by discussion and argument, regardless of where they live, when this is in the cointext of mutual exchange, as here.   

On the other hand I loathe any kind of "cold-calling", and this is a particularly distasteful version of that. The fact that it is in another country isn't really the point, I think, though it does make it even more likely to be counter-productive.

If there were a by-election in England, and an English newspaper were to try the same stunt, I think it would be wrong as well. And if some American newspaper were to try to marshall its readers to write to strangers in this way in some crucial county in the United States, the same objections would arise.

I'm glad to hear that quality newspapers in the USA don't go in for stunts, Doug. I suspect that sometimes British "quality newspapers" have picked up more of the wrong qualities from the tabloid press than they realise, and that isn't by any means true only of the Guardian.