Lots of places have restrictions on how you can say something, but still give wide berth to what ideas you can say. Just because I'm not free to express my distaste for The Last Airbender by punching M. Night Shyamalan does not mean I am not free to voice that opinion. Science journals can require your speech to be in a certain form, namely it must be science, but you are not barred from publishing anything because of what you are saying. While some institutions, like the US Federal Government, might be held to higher standards, this is what most people are referring to when talking about freedom of speech on a platform.