Let’s be clear, the Gulen Movement is not an opposition party; they are a seditious organization. Opposition parties in Turkey, like the MHP, CHP, HDP, etc, participate in the democratic political process, and there is no restriction on them from doing so. The Gulenists seek to infiltrate state institutions to recruit members, indoctrinate people, and gain power and influence through subversive methods, with the aim of seizing control of the government.
The State of Emergency and the expanded powers of the government have been undertaken to facilitate what is necessarily going to be a massive investigatory and judicial process to identify Gulenists from a wide swathe of sectors in the country. The coup attempt was undertaken by a minority within the military, yes, but that minority belonged to a very large organization, and that entire organization is therefore implicated in the coup plot, and thus, its members will be subject to investigation. That is reasonable, in my opinion