I would only trust a tool for sending mass opt-out requests to every company that I've interacted with if it was free and open source. Even with good intentions, commerce becomes yet another tracking instrument.
Not possible. Open source code doesn't have limited power of attorney. Data brokers would also read its code and thwart whatever logic it uses to fill out forms.
Exactly. What we really need is a public, open list of all tracker companies that anyone can contribute to (like adblock lists). What we do with that list is up to us and our governments.
If the open source software interacts with the data brokers as you, then how would it do that without giving up even more of your personal information? Services like Optery also lose the ability to remove your information from a data broker if you have a direct account with them. So you better hope that open source maintainer doesn't lose interest after a while, since if they do, you'll be permanently doomed to logging into hundreds of broker sites each year to refresh your opt-out.