Merely saying you are against SSM is legal. Yes, I'm discriminating. I'm saying only straights have the right to marry. Boo hoo. It's still a legal position to hold and religious institutions are allowed, in the UK, to deny SSM as well, ergo so am I. What should be taught in schools is the basic 'Some folks support SSM and others don't.'It is also illegal, at least in the US, to discriminate based upon sexuality. So there goes that argument.
Because that's the reality.