Yes, I am. That’s something that I do pretty regularly. I take a given set of presuppositions and argue as though those presuppositions are true. That’s not uncommon in philosophy and I think it leads to a better understanding of those who hold those presuppositions. It also lets me know how people who agree with me attack the argument and gives perspective as to where the holes in their arguments are and perhaps where I have been flawed. Sometimes I take the opposite side as a way to wrap around to a different point. I sometimes take a Socratic ‘feigned ignorance’ that leads us to different conclusions. It’s all about a quest for truth.
So, yes. I don’t always stringently argue for beliefs that I think are true. Sometimes I do and sometimes I don’t. The goal isn’t to be ‘right’, it’s about struggling ever closer to what the truth is.
So, for the record, I firmly believe in an objective right and wrong. I don’t know whether preserving biodiversity is objectively right or not, but I am inclined to say that it is. For the sake of this argument though, I will be presupposing that such an objectivity does not exist and all that exists is a physicalist world of process without any metaphysical arbiter of ‘good’ or ‘evil.’
I would also go so far as to say that I more frequently argue against my beliefs than for them. I am not challenging myself when I just parrot the same arguments that I’ve had for the last however long. It doesn’t teach me anything, so I find the exercise fairly fruitless.