I don't think that at any point Eich did not have the right to hold his opinion, just as people and companies have the right to choose not to associate with those who hold those views. Mozilla, and those (internal and external to Mozilla) who are calling for his resignation are not the government are not opressing him in any way.
Whether or not this is the right call for Mozilla is up for debate, but whether his rights were infringed certainly is not.