[seabee]

If there are plenty of good uses for the code, I'd still want to improve it, even if I find out it's used by the Kitten Krusher 3000.

Unless a "please don't use this code for evil" license is legally binding, that's just the nature of open source.

[MrMorden]

A "please don't use this code for evil" license would, by definition, not be open-source. (Also, such a license would almost certainly be ignored by evildoers.)