Does anything need to?
I guess you're worried that if the same argument works in both cases then you might end up obliged to give Joe $1M. But those reasons why you should give Joe the money have exactly parallel reasons why you should keep it, and to zeroth order they all cancel out, so no such obligation.
If you look with a bit more detail, then the reasons might be stronger one way than the other; for instance, if you are quite rich and Joe is quite poor, he might benefit more from the money than you would. We don't generally have norms saying you should give him the money in this case for all sorts of good reasons, but instead we have taxation (compulsory) and charity (optional) which end up having an effect a bit like saying that rich people should give some of their money to much poorer people.
In typical cases, (1) if you give Joe a $1M then your loss will be bigger than Joe's gain, so even aside from other considerations you probably shouldn't, and (2) if you kill Joe then Joe's loss will be bigger than your gain, so even aside from other considerations you probably shouldn't. So the simple-minded "do whatever makes people happiest" principle (a.k.a. total utilitarianism, but you don't have to be a total utilitarian for this to be a reason, as opposed to the only possible reason, for doing something) gives the "right" answers in most cases.
I guess you're worried that if the same argument works in both cases then you might end up obliged to give Joe $1M.
No, I'm claiming neither Kindly nor you actually believe the argument you've given.
So the simple-minded "do whatever makes people happiest" principle (a.k.a. total utilitarianism, but you don't have to be a total utilitarian for this to be a reason, as opposed to the only possible reason, for doing something) gives the "right" answers in most cases.
Except, you're not doing that, i.e., you're not giving all your incom...
Link to Blog Post: "Extremism in Thought Experiments is No Vice"
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