I'm trying to understand what you're saying, let me see if I got it right:

A is capable of helping both B and C, and because he chooses to help B, your argument is that this harms C, because since B is helped, C is deprived of that help.

I have two issues with this.

First, I don't think this constitutes harming someone. Whatever C needs help with, this harm has already been done in the past. Therefore C needing help is the starting point and not a result of A's actions.

Second, as I argued, the neutral situation here is that both B and C need help, and if A only has the capability of helping one or the other, he is still capable of producing a net positive effect where either B or C is helped, instead of both not being helped.

I don't know what "this" is. — khaled

If someone believes they are helping someone, but in fact they are not (the person who is helped does not consent) then the helper was ignorant to the desires of the person who is helped.

The probem with "helping others" is you don't know if you're being an actual help or if you're harming them in some way — khaled

This is why I posit that the valid point you are raising is covered by my point about ignorance in relation to outcomes.

This is why I posit that the valid point you are raising is covered by my point about ignorance in relation to outcomes. — Tzeentch

Yes but you say that if someone had the right intentions but was ignorant and so caused harm, that person is not immoral. But I say, no, they are immoral if they purposely did not ask for consent before doing the act. That’s the only difference

First, I don't think this constitutes harming someone. Whatever C needs help with, this harm has already been done in the past. Therefore C needing help is the starting point and not a result of A's actions. — Tzeentch

Ok, but by not helping C you are causing additional harm by allowing it to continue. If this type of action is permissible, then so are actions like allowing someone to drown, be tortured, etc. If your cook with that, then fine, but I’ve always seen neglect as a type of immoral act. C needs help, and you intentionally not helping causes C’s suffering to continue. Therefore you’re intentionally causing harm, or allowing it to continue, which to me amounts to the same thing since the outcome is the same. Therefore doing so is immoral.

Second, as I argued, the neutral situation here is that both B and C need help, and if A only has the capability of helping one or the other, he is still capable of producing a net positive effect where either B or C is helped, instead of both not being helped. — Tzeentch

Right, but your focus is on intention. So in this situation you are intending harm, or at least its continuation, which according to you is wrong. Unless you want to make a distinction between causing harm and allowing it to continue I don’t see a way out of the issue (other than giving up on intentions being the most important factor).

If this type of action is permissible, then so are actions like allowing someone to drown, be tortured, etc. — Pinprick

Except this would be more akin to a situation in which two persons are drowning and only one can be saved.

I'd say the moral thing to do is to save one rather than to let both drown. I'd certainly not consider it immoral to save at least one.

Except this would be more akin to a situation in which two persons are drowning and only one can be saved. — Tzeentch

Right, but the justification is the same. I guess what I’m getting at is that intentionally causing (allowing) harm is either ok or it’s not. If you try saying it is ok, you end up with conclusions that are undesirable. If you try to say it’s wrong, then there are still situations (I would say many situations) where you have to intentionally cause or allow harm in order to do the right thing (helping someone else).

I'd say the moral thing to do is to save one rather than to let both drown. I'd certainly not consider it immoral to save at least one. — Tzeentch

Well, yeah, we’re in agreement here, it’s just a matter of justifying it in a way that remains applicable in other situations as well. Life just seems too varied to apply any type of moral justification across the board in any and all circumstances.