Your post appeared to be framing both reactions—to Smith (by you) and to Zegler (by others)—as indifference:
It's indifference. Example, I thought what will Smiths slap was disgusting. I won't ever see a Smith movie in a theater again. It's simple, it doesn't mesh with my values so I just ignore what he does. And to think that's not happened with Zegler, is a bit naive in my opinion. It's easy to not support people you don't like. And you don't even need to be outraged.
You may feel indifferent towards Zegler, but those choosing not to see the film
because of her by definition cannot be, just as you, as you acknowledge, are not indifferent towards Smith.