Lacking evidence otherwise, I would say that we have to assume the internal experience of most life with central nervous systems are remarkably similar to ours, because we are remarkably similar.

The next step is to take this into account in ethics, but I fear this is a leap that humanity in totality will not make easily.

I agree. It’s like we forget that we’re literally one of millions, billions, or trillions (it seems the estimated count is an open question) of species on this planet. No other species could possibly share analogous behavior.