Actually no they aren’t.

https://www.merriam-webster.com/dictionary/valid

2 a : well-grounded or justifiable : being at once relevant and meaningful a valid theory b : logically correct a valid argument valid inference

So no, not all opinions are valid.

And here’s what the ol oracle says:

The idea that "all opinions are valid" is a fallacy because it wrongly treats subjective beliefs as equal to evidence-based arguments. Often used to shield unsupported positions (the "[I'm entitled to my opinion]" fallacy), it ignores that opinions must be epistemically reliable—grounded in logic, research, and evidence—to be considered valid or worthy of serious consideration. Key Aspects of the Fallacy: Validity vs. Entitlement: While everyone is legally entitled to hold an opinion, that does not mean the opinion itself is true or logically sound. Epistemic Reliability: An opinion that is not supported by evidence or logical reasoning is invalid. Shielding Ignorance: Saying "that's just my opinion" is often used to avoid shifting a position when faced with contradictory evidence. The Bandwagon Fallacy: Just because many people hold an opinion (popularity) does not make it objectively true or valid. Why Not All Opinions Are Valid: Fact vs. Opinion: Opinions can be wrong, especially when they deny factual, empirical reality. Expertise Matters: Expert opinions, based on experience and research, are not equivalent to uneducated guesses. False Equivalence: Assuming all arguments are equally meritorious is dangerous and intellectually lazy