Consider two questions:

1. If I push something off of a five foot ledge, will it take longer to fall than if I push something off of a one foot ledge?
2. If a doctor could save five lives by killing one person and distributing their organs, should they do it?

Both questions take a complex situation and reduce it to some simple facts, right? But they feel so different! Why?

In the first most people will accept the facts and the abstraction. You could ask about air resistance, knowlege of the relative ledge heights, or whether the reference frame is inertial, but they're clearly not important. The question reduces to "do things take longer to fall farther?", and people feel comfortable responding "yes".

In the second, however, while some people will just say "no" and a very few will just say "yes", most people will want clarification. How does the doctor know the organs won't be rejected? Will other people find out and start avoiding doctors? Even if the person proposing the hypothetical gives answers that keep the problem tidy (the doctor is very reliable, has run lots of tests, no one will ever know what happened, ...) most people still won't be satisfied or give a yes/no answer.

This tendency for people to look at morality questions and reject the abstractions of the hypothetical annoys philosophers, but it's actually valuable. We examine simplified problems so that we can understand what's important in dealing with the real world, but whether this is helpful depends on whether the simplified problem captures what's important.

A very common simplification is that you're completely confident in the facts of the matter. You're told that killing the one will save the five without any future effects. But any morality for real humans is and must be a morality of uncertainty and bias. We need to take into account that even when we're really sure of things there's a substantial chance we're wrong. We naturally fight hypotheticals where we're asked to assume we have perfect certainty, and this is a very healthy reaction.