I spent some time on reading about why should one person's opinion matter and freedom of speech and rights. As you may be aware, there is a non-religious theory called the Social Contract that was developed in the 17th century. Many of the constitutions are based on it, including the US constitution which follows the Locke version of this theory and I will talk about it in a bit. All the variants start with the assumption premise that there is a state of absolute freedom, but in order to form a civil society you have to give up some of it so that you can co-exist and co-operate.
The Hobbes version of the theory says that you must give up some of your rights that existed in your natural state so that I can cede mine and we can live in harmony. In our case this would mean that I agree not to dis you so that you don't dis me.
The Rousseau version of this theory says that it is the collective will as opposed to egotist considerations that decides what is wrong or right and then we become a part of that and the collective will decide what is wrong or right (laws). In our case it means that if there is a law against religious slander so that different religions can get along then they should be applied to this case.
The Locke version says that giving up of rights happens naturally when people make a moral decision not to hurt each other and come together to create a state which need impose no restriction on their rights. In this case it can mean anything. Someone will say, as in a recent post here, my morals and rights allow me to 'mock any religion, question every belief and if you don't line it, it is your fault because you are easily offended'.
Now US constitution adopted this concept at time when it was a small, homogeneous population that wanted to cede from a much larger empire. We have seen in recent times that as the nation got bigger and heterogenous, people do not have the same notion of what 'moral' means, some people downright do not want to be constrained by anything and want to be in the 'natural free state' which is not possible unless you live on an unconnected island. We need to evaluate the Constitution and see what still is applicable and what is not. We have seen the result of not doing this in numerous free speech abuses and once you think a little bit another right that has harmed innocent civilians and claimed many lives comes to mind, but off topic here.