One objection to the notion of moral responsibility is one of determinism. That is, if we can't help do what we do, then we are not responsible for it. Discussions about materialism often hinge around the assumption that if it's all physically determined there's no sense to have moral responsibility.
But physical determinism isn't the only kind of determinism out there that people use to take away moral responsibility. Biological determinism, and societal determinism both plays roles in diminishing our sense of responsibility of action. So I want to write a short list of the kinds of determinism out there, and how they are perceived to undermine that sense of responsibility. Whether they do or not, that's another story. But for now here are the main factors to consider.
* Physical Determinism
Physical determinism can be summarised as everything that happens in the universe is determined by the prior state of the universe. Thus as physical beings, we have no control over what happens - what happens is determined by the jiggling of atoms in accordance with fixed laws. Thus for some, there is no responsibility in determinism, for how could things be otherwise?
* Biological Determinism
Biological determinism can be summarised that many of our impulses and behaviours are caused by genetic and epigenetic factors. The question of the permissibility of homosexuality centres around whether homosexuality is actually a choice, that is to say that people are through biological factors gay.
* Cultural Determinism
Cultural determinism can be summarised as that someone is a product of their culture to the extent that cultural beliefs and practices dominate the behavioural outcomes of the individual. Someone brought up in a culture that taught racism, for example, would turn out racist themselves. Social problems are often blamed on units of culture, like violent television, music, or video games, that are seen to be the negative factors that cause crime.
* Circumstantial Determinism
Circumstantial determinism can be summarised as that someone's circumstances in life are what lead to behaviours. Abused turn into abusers, poverty perpetuates poverty, criminals breed criminals; in other words, the positive and negative aspects of one's life are dictated by the prior circumstances in their life.