I'd like to play the devil's advocate here for a moment. I'm not entirely sure how I should respond to the following argument.

The second thought – that we try to make things better – is shared by every plausible moral system and every decent person.

That begs the question: people often disagree on what is a better state of things. (And of course they say those who disagree with you are not "decent".)

Don't ignore the fact that people agree on only a very small set of altrustic acts. And even then, many people are neutral about them, or almost so, or they only support them if they ignore the lost opportunities of e.g. giving money to them and not to those other less fortunate people.

The great majority of things people want, they don't want in common. Do you want to improve technology and medicine, or prevent unfriendly AI, or convert people to Christianity, or allow abortion, or free slaves, or prevent use of birth control, or give women equal legal rights, or make atheism legal, or prevent the disrespect and destruction of holy places, or remove speech restrictions, or allow free market contracts? Name any change you think a great historical moral advance, and you'll find people who fought against it.

Most great causes have people fighting for and against. This is unsurprising: when everyone is on the same side, the problem tends to be resolved quickly. The only things everyone agrees are bad, but which keep existing for decades, are those people are apathetic about - not the greatest moral causes of the day.

Does selecting causes for the widest moral consensus mean selecting the most inoffensive ones? If not, why not? Do you believe that impersonal and accidental forces of history generate as much misery, which you can fight against, as the deliberate efforts of people who disagree with you? Wouldn't that be surprising if it were true?