You seem to not understand what moral nihilism is, so let me indulge you in my brain:
There are way too many meta-ethical schools of thought to cover here, so I'll just cover some of the basics (to the limits of my understanding).
On the most extreme side we have
Moral Absolutism, adherents of which will claim that morality is an perfectly objective standard of morality with definitive existence within the universe. Those who adopt such a meta-ethical philosophy are, from my perspective, usually highly religious and literally interpret whatever scripture they follow as the Absolute truth of humankind. The big glaring issues I have here are three-fold:
1) Each proponent of a morally absolute doctrine will enforce rules that often differ radically from each other (if morality was objective, wouldn't there be just one law that everybody followed naturally?)
2) Such rules of law often place too much dependence on authority to set and enforce these rules, which ends up being more morality by force and punishment rather than personal obligation or "greater good"
3) Different groups or individuals will often interpret these so-called "objective" truths in radically different ways, each one claiming their own subjective interpretation of the precedent as the Truth. Just look at all the sects and denominations of Christianity in the U.S. today, the specific teachings of which all derived from the same one book. This sort of thing starts wars when left unchecked...
On the opposite end of the spectrum we have
Moral Relativism, which establishes morality as a matter of subjective interpretation based solely on an individual's life circumstances like culture, gender, experiences, etc. For me this works as a more reasonable compromise down from moral absolutism, but this forces me to ask the question: if right and wrong are determined solely on the individual's perspective, then what's the point in trying to classify it? If any moral debate you have between two people ends up in "I think it's right" vs "I think it's wrong, but I understand that morality depends on the individual," then nobody has learned anything. Any attempt at legitimate discussion just turns into a passive, inoffensively feel-good slumber party where the opportunity to learn something new about yourself or the world can't possibly develop.
Despite the radical and irreconcilable differences between these two meta-ethical standpoints, they both deal with the same issues of right vs. wrong, good vs. evil etc., and both accept that right/wrong, good/bad dichotomies exist in some form or another. So I ask, how does one define "good" or "bad" in the first place? This is, of course, the exact question the entire field of Ethics attempts to solve. But this field, like the greatest majority of religions, lacks something incredibly important about its foundations: measurability. How can you measure a thing's goodness in an objective manner? There exists no moral spectrometer that can give a readout of how many righteousness-waves some bloke emits when he gives a homeless kid a fiver. The only way a person can determine goodness or badness is through some other secondary or tertiary means of interpretation, either by precedent (people say that X is bad, so I won't allow it), authority (my book/priest/markov chain text generator says that Y is good, so I accept it), or through some other personally-devised structure of understanding. None of these methods of understanding deal with the object itself as the focal point, rather the method by which the thing is interpreted.
At this point, I find myself rather disinterested in debating whether or not something is morally correct because the means by which people attempt to gauge morality depend on what method they use to interpret it rather than the physically observable consequences of the thing itself. The reason for this, I contend, is that right and wrong do not exist in any sense other than linguistic practicality. Any interpretations of right and wrong I automatically translate as "I like" and "I dislike," because to my ear that's all they're saying. Without some sort of physical display of what good or bad looks like, all that can be said about the matter lives in the projections that people create in its place. Basically my understanding of other people's ethical reactions falls mostly under what @
Taknamay posted about Emotivism.