Those pushing for racial equality are similar to those pushing for sex/gender equality within marriage or equality in how different sexualities are treated. Those who are for treating the genders/sexes differently when it comes to marriage or the different sexualities different when it comes to other issues are the ones who are not following the Golden Rule. You cannot possibly say that trying to legally prevent people from being allowed to legally marry or adopt/raise children just because someone believes it is a sin, despite not doing the same thing to others who sin, is "doing unto others as you would have them do unto you".
It doesn't matter if it is only a little bit, the ability to reason is still found in our DNA.
Wrong. Every person has some ability to reason, even if it is very limited, unless they had some environmental issue take that ability away from them, which would have them living a life which required someone else to do things for them. In order to learn very basic tasks, such as feeding ourselves or getting dressed or even communicating with each other, a person must have some very basic reasoning skills.
We don't know. It could have been either of those. That is a question people have been asking themselves for a long time and has very little to do with the OP, since no one knows what caused us to have a conscience, and even if it were a god/higher power, that does not mean that it has to be the God/higher power that certain groups of people believe in.