Only unethical if you obscure the fact that people are signing up for a recurring bill and/or hope they forget to cancel despite not using the service.
I've not seen it obscured. Its difficult to read a person's mind to know I'd they forgot to cancel or actively remembered they had a subscription.
Yes but you designed in such a way that the users intent is obscured and assume the intent that benefits you.
If you just don’t auto-bill and ask them for confirmation after the trail then you know for sure.