But also realize that you aren't trying to sell the game to yourself. If someone suggests something, odds are, they won't be alone in wanting it. If it's possible to add an option for mouse control, why not add it? Give people the choice to play like they want to. It costs you almost nothing in development time and it has the potential to increase your sales market (more people are happy, more positive word of mouth, etc).
A fair point, and in some respects I would agree. I've already done this to an extent with things like the tutorial mode. The key factor for me in a decision like this is that it can only add to the game, so why not add it indeed?
But if it's actually rather unwieldy and unpleasant, I feel there is a valid reason for not adding it. Adding such a feature detracts from the whole and taints the entire product. Particularly with mouse control, since it's the primary input device for a PC, so it tends to be the one you try first. If just a few people like it better and buy because there's mouse control, that's a win and it was worth doing. But if just a few don't like it and ditch the game without trying it with another controller, that's a lose. Shareware buyers can afford to be fickle. They find one thing they don't like, they didn't pay anything for it, so they ditch it and try something else. I don't want those kind of weak points.
And to reiterate, Ban is the only, single person who asked for mouse control. No one else mentioned it, or even took an interest when I suggested I would try adding it.