"Thirdly, there are practical reasons to oppose copyleft. Namely, when I publish source code, one of my main goals is for as many people as possible to use it, regardless of whether it's other individuals or giant corporations."

This seems to be possibly the most salient reason people who otherwise oppose copyright oppose copyleft. This is a conflict between people who are ideologically liberal who are attempting to engage in a kind of left politics. They display willingness to allow corporations and capitalism generally to exploit their work on their own terms without giving back. They generally accept the economic order.

On the other hand, if you are a committed anti-capitalist: who care? The corporations, the bosses, the exploiters. They should all perish from the earth anyway and we should feel absolutely free to use the system they constructed against them and for each other.

Our own individualistic tactics of not partaking in distasteful systems is idealistic and due to the power imbalance will not amount to much. Only tactics that force decisions and build dual-power communities can correct such a situation.

Bear in mind that if we decide to use copyleft as a tactic against corporate rule en mass, it is flawed as it is to use the power of the state against corporate interests which own the state. This is a severe limitation because if it becomes enough of a hindrance, the state will just pass something like a "national security" exception to copyleft and every defense contractor and company over a certain net worth will qualify.