Political sectarianism is Unionist trait?

Eoin Ó Murchú argues that political sectarianism only exists in one direction. To that extent he notes that only Unionist dominated councils have they refused the principle of rotation of offices with all major parties: Strabane and Down’s nationalist dominated council recently elected DUP men as Chair this year for the first time. Although the DUP in Castlereagh has finally bitten the bullet and elected SDLP man Brian Hanvey as Deputy Mayor. However, there is no real coverage of the topic mentioned in the headline: ie the linkage to actual violence. Something which is considerably more ambiguous than the public political positions of the two main parties.