"Respectable" of course means that the subject can be integrated with polite society. Respectability is a strong precondition on ability to have open influence in the mainstream.

Thus the Overton window becomes a mechanism of political control. If you can define the coordinating ideologies of all enemy political coalitions as outside the Overton window, then respectable society, which is your own power base, will be free of their influence, and they will be fatally marginalized. It is difficult to get your people to play along just by fiat, but it can be done. This is the basic insight behind official ideologies and religions, inquisitions, political repression of speech, and so on. It is an indispensable system of power for any ruling coalition, and is thus present in all societies.

The trouble with the Overton window as a mechanism of political control, and with politicization of speech and thought in general, is that it causes significant collateral damage on the ability of your society to think clearly. If some thoughts are unthinkable and unspeakable, and the truth happens in some case to fall outside of polite consensus, then your ruling elite and their society will run into situations they simply can't handle.

Thus a wise elite uses the politicization of speech very sparingly, only in situations where immediate political security is threatened, and they use it in concert with other destructive but effective mechanisms like martial law, state seizure of assets, and such, to quickly and decisively return to a state of political security. Once political security is restored, the lawful freedom which is necessary for clear thought and prosperity can be reinstated.