The case for it appeals to standard premises that sound plausible when you hear them. There is no standard reason people reject it in the philosophical literature—no objection that is widely agreed to succeed.
That is probably true if you only look at the philosophical literature. But outside of a few small groups such as that, people widely reject the premise that we should have identical moral concerns for people in the distant future and people currently alive.
Premises that are truly widely shared only support a weaker version of longtermism than yours.
Even if future people matter .001% as much as present people, the argument for SL goes through.
Also, it just seems bizarre that the moral importance of a person would depend on when in time they exist. If someone time-traveled back from the future to the present, would it start being 100x worse for them to stub their toe?
That is probably true if you only look at the philosophical literature. But outside of a few small groups such as that, people widely reject the premise that we should have identical moral concerns for people in the distant future and people currently alive.
Premises that are truly widely shared only support a weaker version of longtermism than yours.
Even if future people matter .001% as much as present people, the argument for SL goes through.
Also, it just seems bizarre that the moral importance of a person would depend on when in time they exist. If someone time-traveled back from the future to the present, would it start being 100x worse for them to stub their toe?