There’s no contradiction between politics being how people make collective decisions and people having an agenda. The differing agendas are part of what make coordination difficult and conflict likely.

Even when goals are the same you can have disagreement over how to achieve them. When goals and values are in conflict, i.e. people have different agendas, we need a mechanism for deciding how to end these conflicts. That mechanism is politics, expressed as some combination of persuasion and violence, how we form, sustain and define communities.