It's a spectrum. You can't ban left wingers and right wingers because there's no one remaining.
The spectrum probably needs updating, more conservative vs progressive these days, but where 'centre' is depends on your perspective.
In terms of the US, my view is that the Democrats are slightly right of centre, Republicans are so far down the right wing fascist path that their whole democracy is stuffed, and the only true left wingers left are individuals like Bernie Sanders.