Against Nihilism This is the statement I most disagree with: "simply because to assume otherwise would just be to give up for no reason" but I'll get to that later.
I don't think this is arguing against nihilism logically but pragmatically: "I object to that on the grounds that if it is true, then by its nature it cannot be known to be true because to know it to be true we would need some means of objectively evaluating claims about what is real and what is moral"
Nihilism doesn't exclude itself from its own equation. It doesn't claim to be objective. It claims that all beliefs (including this one) are relative and believed in by the person's choice. To disagree with it is just that, disagreement, it doesn't prove it false. It's a statement that, whether you agree or disagree with it, remains unprovable. It cannot be established objectively but neither can it be dismissed. So your argument against Nihilism is purely a pragmatic one. "We can either give up or go on" is what it boils down to but that doesn't logically disprove anything. You can't logically respond to the people that choose to "give up".
Also, another interesting thing I find with your argument against it is that, whether or not one believes there is nothing real or moral, they will take very similar steps from that point.
"or, instead, we could baselessly assume that there is something real and something moral — as there certainly inevitably seems to be, for even if you are a solipsist and egotist, some things will still look true or false to you and feel good or bad to you — and then proceed with the long hard work of figuring out what seems most likely to be real and moral, by attending closely and thoroughly to those seemings, those experiences."
How exactly would one go about figuring out what seems most likely or real WITHOUT employing some sort of arbitrary system of evaluation? The system you proposed sounds to me like trying to reconcile all the different views, to find common ground among them. But how is that different from the initial position you disagreed with of saying that the closest we can get to objective morality or reality is whatever the group agrees with? Because to me, they sound exactly the same. And that's why I disagree with: "simply because to assume otherwise would just be to give up for no reason."
People don't go: "There is no objective reality I'll just kill myself now" they usually go "There is no objective reality so what's the next best thing?" And end up doing the exact same thing as people that say "There is an objective reality time to find it"
That's why I usually don't bother getting into threads that have "Is there an objective X" because:
1- To assume there is or there isn't is just as baseless
2- Whichever you end up going with you practically do the same things
In other words, answering the question is pointless.