I think ISFP's, since they do lead via Fi can definitely be somewhere in the middle of, agreeing with consensus, holding back opinions when it's not of dire concern, in order to get along with others and being fierce about their ideals. I don't think they contradict one another. When it matters, we stand up for what we believe in. When it doesn't matter, there's not any real reason to worry about trivial things, especially since everyone is entitled to their opinions.
Think... Harry Potter. My favorite ISFP. He stood up for things that were important. We're not the type to go around jumping into debates with people.