Argument from Conscience

[RobbyPants]

1) Each person is obligated to follow his or her moral conscience.
2) The human conscience is the product of something: either instinctual nature, the individual, society, or divine.
3) No one is morally obligated to follow instinct since instincts easily fail upon rational consideration.
4) No one individual’s conscience is absolute and morally binding on others.
5) Individual consciences cannot be added together unless each person relies on their own conscience to feel morally obliged to the group. Thus it is functionally equivalent to individual conscience as a source.
6) The only remaining source is something that transcends nature, the individual, and society. Such a source must be divine.

#5 is the obvious weak point:

There are logical, secular reasons for people to work in a group. On top of that, we may even have "instinctual" reasons to work as a group, as well. Collective "morality" may very well be nothing but similar opinions expressed in aggregate, and you have done nothing to prove that this isn't the case. Further, this notion is supported by times that society changes its opinion on moral issues (see: slavery, the civil rights movement, and gay marriage, to name a few).