I disagree. Any form of discrimination is harmful - it is saying to someone that they are entitled to less than someone else, because of the colour of their skin, or their gender, or their sexuality, or some other feature. It is deeply hurtful, and wrong in one of the most fundamental ways that something can be wrong.
I will agree that telling Christians that they will be held liable, if they discriminate in accordance with their faith, can be seen as imposing harm on Christians, in that they see themselves as being required to act against their conscience. However, what happens then is that we balance the harm to the person being discriminated against, with the harm to the Christian of acting against their conscience. I very firmly believe that the balance comes down hugely in favour of the gay couples whose sexuality is being discriminated against, rather than the Christians, who believe that someone else's un-chosen sexuality is a sin and an affront to their own opinions.
At its most basic level, you don't get a free pass to discriminate against someone, just because you believe that God said they're sinners.
Could there be any greater conceit, than for someone to believe that the universe has to be simple enough for them to be able to understand it ?