Why do you assume I don't? Opinionated defaults matter, as that's what most users will end up using.

Would you be ok if stores offered the option between a cheap plastic bag and a more expensive non-plastic one? (All the stores here already do it, btw).

I think the externalities of plastic recycling must be internalized economically by requiring all manufacturers of items to pre-pay for the recycling of said items up front, as part of the manufacturing cost. Similar to how bottle returns are managed, which has been very successful. Items which are provably biodegradable or designed to facilitate repair may be exempt.

Plastic bags are already taxed where I live. Consumers pay that tax, obviously. Other costs imposed on producers of plastic items will just be passed down to consumers.

That's lovely, but it's not what I described. Bottles aren't just taxed. They have a refundable deposit. This ensures they don't end up in a landfill.

Exactly. The point of this sort of tax should not be to collect revenue, it should be to ensure that non-biodegradable bags are being disposed of correctly. To the extent that this is not happening, any bag tax is malfunctioning. Such a tax is either insufficient or poorly-designed. (Our city just banned chain stores from giving out plastic bags under 4 mils thick, and stores now give out paper and sell re-usable bags.)