When you say, "all opinions are equally valid", what does the word "valid" mean?
It seems to be this word is doing a lot of work and if you explore this your position will quickly collapse.
Opinions are generally about moral issues - what we should do, what goals we should pursue. They are not about positive facts like "how many people live in America".
In the arena of goal-setting there are indeed no objective facts. It is equally valid to want to pursue a global caliphate where all women are slaves to the men who own them and all gay people and apostates are executed, as it is to want to pursue a global social justice utopia (however you could even describe such a thing). There is no objective standard to reject either goal. There are simply preferences.
What's more prefereable? Killing an unborn fetus at 3 months development, or obligating a mother to carry it to term? Why? How can you possibly say that your preference is objectively true? It obviously isn't.
If you think your preferences are objectively more right than others, you need to explain what part of the nature of the universe makes it so. (Incidentally religious people have this explanation - it's because the creator of the universe declared that these are the best preferences.)
If you want more reading, you can look up the difference between positive and normative beliefs.
Your goal here is just to set up a system where the people with power, who happen to agree with your preferences, get permission to punish people who disagree with their preferences. This is 100% a belief conditioned on the fact that you know that people like you have the power. If the people with power disagreed with you you'd be a free speech advocate (as people of your opinion were a few decades ago).
There is in fact no way to objectively set up a policy of "Allow the right opinions, and punish the wrong ones" and it's childish to say you can.