I don't think people unfamiliar w/ UK and Irish politics are necessarily getting the full context and are agreeing to a hypothetical celebration of the downfall of the UK.

Which is fine, but let me explain because it's actually very important that we as leftists know this. Northern Ireland has been under British colonial occupation for 101 years and as such, is part of the UK. Mary Lou McDonald, of the Sinn Féin party, is an Irish Republican, ie socialist, and wants to unite Northern Ireland and Ireland. This would be an incredible and historic achievement of the Irish gaining total freedom and independence from British colonizers.

Piers Morgan, as is obvious, is a right-winger with reactionary politics who is crying on Twitter about the idea of a united Ireland because he believes it would "collapse" the UK. Which is all good and well as far as I'm concerned. But also as leftists we should absolutely cheer on McDonald's victory and the campaign for a united Ireland as we should for any country under colonial occupation to gain its independence.