It's not for either your investors or your customers to tell you what to build anyway.
And just never talk about morals, which I deem "fluff".
You can (and should) get a sense of which ideas are worthwhile, but you'll never know for sure. Maybe your potential cure for cancer won't work. Maybe your todo list app will help 100 medical non-profits each be 5% more efficient, in effect having 5 non-profit's worth of impact. With that in mind, the best you can do is pick something that you can probably make work, that people probably want, and that will probably have a positive impact on society. Whether or not you change the world is up to the gods.
No. Take some responsibility (and therefore, credit) for your actions.