>Are the arguments against objective ethics/morality, motivated by persons unable to deal with shame and/or thier previous bad decisions?

Some might be, but others are motivated by the fact that those who advocate for an objective morality almost invariably have extremely poor arguments for their position. In other words, those who advocate for objective morality tend to not prove their position, and we are left wondering if their failure is due to them being just wrong. If it is objective, like other facts, such as rain falls from the sky, a demonstration of some type ought to be given, yet that isn't done, and they almost always end up appealing to someone's feelings about facts, rather than demonstrate some fact that is morality. Which suggests that what they are doing is really subjective instead of their claim that it is all objective.

Of course this also depends on how, exactly, one defines "objective" and "subjective" for morality. If, for example, we look at something like David Hume's ethical theory, what determines right and wrong are feelings, but not simply one person's preferences. It is based upon feelings of empathy, that are shared among people who are not regarded as psychopaths or sociopaths (and whose feelings are not corrupted with false beliefs). So, is that objective, since it is felt by many, or is it subjective, because it is based on feelings?

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If anyone wants to read what Hume has to say about ethics, a good place to start is his Enquiry Concerning the Principles of Morals which can be found here (among other places):

https://davidhume.org/texts/m/