The right thing to do is to pull the lever, diverting the trolley onto the side track where it will kill one person.
You should pull the lever because five lives are worth more than one.
You should pull the lever because a world where people are willing to sacrifice one person to save five is a safer world to live in overall.
68% of professional philosophers would sacrifice the one person. In an ethical question their opinion is a good guide (Bourget & Chalmers, p.16).
Pulling the lever can lead to direct benefits.
Because each person has a greater chance of ending up on the main track than on the side track, each person would presumably agree to throw the switch in the event they were to find themself in this position.
A human being is an end unto itself — individuals should never be treated as a means to an end. You shouldn't pull the lever because that makes one life a mere tool to save others.
Pulling the lever leads to six people who will feel responsible in the taking of another human life, for the rest of their lives. This is likely to generate more harms overall than the other scenario.
By pulling the lever, you actively interfere with fate/nature/Higher being's plan, which is wrong.
If self-sacrifice for a greater number of people is not an obligation, then sacrificing someone else to save a greater amount of people without their consent cannot be the right thing to do.
By pulling the lever you actively cause someone to die. That is wrong.
It is better not to act because of a lack of sufficient information.
You do not know any of the people involved. Thus you should not care at all and abstain from making the choice.
If the bystander is unsure of what to do, they should not pull the lever.
Roll a six-sided die. If 1-5; Pull the lever and save the 5 people. If 6; Be passive and save 1 person. This way every individual's wishes are equally valued, instead of totally dismissing the wish of the single person or the five people.
The moral duty not to interfere with someone else's capacity, in this case that of the one to continue living, is superior to any moral duty to rescue someone from their own incapacity.