The real question here is for atheists:
What or where do you derive your moral principles from?
Your question assumes I must have a predefined set of moral principles. Thus your question is flawed. I take a centric approach with decisions, but am very mindful of "karma" type effects. In other words, I make decisions that advantage me, and those I care about, but I am fully aware that if i do harm (of any kind) in the process, that it could eventually come back to haunt me (or harm me during the act of doing harm). I guage these potential harms vs benefits and act (or not act) accordingly.
I like to think that, in theory, all options are on the table. "Moral principles" to me suggest that some options are simply not there, and I interpret that as weakness. If you have a rule i dont, then that means i have the option to do something you cannot (unless you have no moral absolutes).
Now i know this sounds pretty evil, but its really not. I'm an emotional creature just like all of us, and i also have empathy, so sometimes the "greater good for me" might be helping a person in need. Someone else obviously benefits from it, and I as well feel good because I helped someone. So win/win. No predefined rules, but still not an uncommon occurence for an atheist.
Are they subject to change based on individual circumstances?
n/a per my answer to your first question.
Do you believe that there should be a moral standard that a society cannot cross?
I dont particularily have any problems with the existence of "moral standards" either self imposed by the masses (such as via a religion) or via laws. If these things did not exist, then i would no longer have the advantage that i do, due to their existence. These also have a host of other benefits, like keeping the masses pacified when they might otherwise be volatile.
I'm a scientist so just generally speaking, i do not like absolutes. Everything's negotiable. Lets sit down and look at the pros and cons.
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This discussion reminds me of the movie "Crash"; movie of the year last year. There's a lot of interesting moral topics dealt with in that movie, in particular how morality seems to be throw in the grey area. I liked that because i think it emphasized that morality isnt quite as cut and dry as many of the fundamentist would like to believe it is.
Anyone like ad&d? If i were to have to pick an ad&d alignment for myself, it would be chaotic neutral.
Azanon
(edit) cutthroat mentioned ebay. For the record, i currently have 11 positives, 0 neutrals or negatives. So I guess there's another example of an atheist being dependable. Common sense tells me that if i screw someone, they are going to click negative and then i will only be able to sell two types of items afterwards; 1. jack and 2. s*it.