One can't condensate it all as to "do no harm". Inaction can also cause harm.
Also, using the trolley dilemma example for the sake of the argument, it isn't there to give you a definitive solution to a problem as old as time. It is there to prove a point, it being: it depends.
Laws (as a set of rules to follow in society in comparison to our personal moral values) are more effective in some places than others, for example, because of a plethora of reasons and not just because of how they were written or how they are enforced, but it also doesn't mean that we shouldn't create them and follow them.
It is tiring to seek these answers and try to apply them to our personal lives because most of us have the "efficient market utilitarian" based approach to suffering, in which we avoid it at all costs while externalizing the labor of it somewhere else without considering the consequences. Point being, as presented by Zizek, paying Starbucks a few cents per cup to fight global warming. As things are, you can't avoid harm. It has to go somewhere.