Open source licences IMHO should be viewed not as agreements, but as offers of agreement.
You're free to accept the offer, which then implies certain obligations described in the agreement.
You're also free not to accept the offer, which implies the default conditions set by law, i.e., copying and distribution is prohibited without explicit permission of the author(s). For example, anyone certainly can ignore the provisions of GPL and redistribute the software as closed source if they have obtained some other licence from all the authors.
You're free to accept the offer, which then implies certain obligations described in the agreement.
You're also free not to accept the offer, which implies the default conditions set by law, i.e., copying and distribution is prohibited without explicit permission of the author(s). For example, anyone certainly can ignore the provisions of GPL and redistribute the software as closed source if they have obtained some other licence from all the authors.