"Isn't ethics just about opinions?"
Questions of this kind often reflect students' notions about ethics being merely subjective.
It's advisable to nip these notions in the bud and to make it clear to students that though ethics may seem to be subjective, and though there may be a subjective component in our deliberations regarding ethical issues, ethics is not merely subjective or an expression of emotions.
Here's why:
Subjectivism is the view that moral judgments merely state or express the emotions or preferences of the speaker.
For a subjectivist, there is no need to give reasons for one's belief about ethical claims. To say that x is wrong is to say nothing other than that one doesn't like x.
So, for example, to say that racism is wrong is to say nothing more than that the speaker doesn't like racism.
And this is a problem.
There are a number of serious objections to subjectivism. Here are just four:
1. If subjectivism is true, then the opinions of those in power are more easily forced upon others, while those who may oppose these opinions have no recourse to any "objective" grounds for objecting to these prevailing opinions. In other words, if subjectivism is true, then "might makes right".
2. If subjectivism is true, then there is no possibility of anybody being wrong; there will only be differences of opinion and preference.
3. If subjectivism is true and ethical claims express nothing more than our own attitudes about a particular act or behavior, then genuine ethical disagreement would be impossible.
4. If subjectivism is true and ethical claims express nothing more than our own attitudes about a particular act or behavior, then neither would any genuine ethical agreement be possible.
Students confronted with these objections may not immediately reject subjectivism, but in responding to their concerns in this way, you can help them see that their view reflects an implicit (and problematic) framework.