> There are so many laws, I don't know how you could possibly say in an informed manner that you agree with most of them.

Oh, come on now. You can be informed on the ones that matter to you the most, and the ones which are most commonly broken, which says a lot about the society you live in. It's not that hard.

> I don't see why we should factor the law into discussions of ethics

Because laws, in many or most cases, reflect the moral or ethical views of a large number of people, or at least they did at the time they were passed. The fact that laws survived the lawmaking process at all means we should consider the thoughts that went into their creation. I'm not saying you should read every word of every statute. But a nation's laws are in many ways reflections of its cultural ethics.

The laws that "matter most" reflect ethics which are "no brainers". "Don't steal", "don't kill", "don't rape", etc.

These are ethical concepts that are easy to understand without resorting to consulting the law. The law in these cases is just an imperfect encoding of these obvious ethics. For the sake of governing, they work decently. However using them in an ethical discussion is using them for a purpose that they were not designed. There are so many better sources that we can look to in order to facilitate discussion.

Trying to use laws as a vehicle to discuss ethics is like examining Cheese Wiz to learn about dairy.