Hi Tucker, thanks for all the recommendations, they seem promising indeed :)
I agree that we should only use the word "should" if that's helpful, but I didn't go as far as saying that in my article because at this point it strikes me as unreasonable to expect this word to disappear any time soon. I think it would be a good idea to try and use a moral language that is as non-judgemental as possible, but I think this will be a slow process, and honestly I hope that it will happen in parallel with another process: people becoming more mature and less defensive. I don't tell people that they "should" go vegan, but if somebody tells me that I say "in a way I agree with you", and I try not to get defensive. I think both things are important.
As for the distinction between forgiveness and excusability, perhaps I missed the nuance as a non-native English speaker, but what I meant by "being forgiving" is basically "not being judgemental". I think it's not productive to give people the sensation that "they are not doing enough" even though they are already doing quite a bit. I only think it's fair (or almost inevitable) to appeal to guilt in extreme cases, for example to convince a hardcore carnivore to have at least one vegetarian day per week, or a rich ostentatious playboy to donate at least a small percentage of his wealth. But for people who already have a level of awareness and try to live a reasonably sustainable life, avoiding meat and recycling etc, I think it would be counter-productive to shame them into going fully vegan or zero-waste. Of course I will try to be careful even in extreme cases, but it's almost impossible to make my case in a way that is honest and not manipulative without invoking at least some level of guilt. If I told them they have no reason at all to feel guilty, I would be lying.