Your assumption that can only be used to express your own desires is the problem here.
> Verb in -form + = Want someone to do verb
The person you want to do the verb (if they are mentioned) is marked by , e.g.
>
> I want Yuki to teach me Japanese.
Your sentence:
>
> We want even people who've never donated before to have fun making a donation.
Note that the people they want to do action are not marked by here because they have been promoted to the topic of the sentence (but with replaced by ).