In Russian, there's a distinction between русские (ethnical Russians) and россияне (Russian nationals/citizens) which doesn't map to English well - it's Russians either way in it. This slogan implies the former (ethnical Russians), and was declared extremist long ago, for a reason.

This distinction is a very frequent source of misunderstanding for both native speakers and English speakers, as Russians might hear one where you imply another, and vice versa.