"When did it become a crime to have a different opinion?"
First of all, stop being so fucking dramatic. You've yelled at people for "having a different opinion" over trivial shit, I know you have, because we ALL have. Second, not all opinions are the same. There are plenty of opinions to have over things that are NOT trivial.
Let's consider what an opinion actually is. The word has become largely meaningless from misuse, but the technical definition is "a view or judgment formed about something, not necessarily based on fact or knowledge." Still pretty vague. Something this broad can't possibly avoid being harmful in all cases. You could easily hold the opinion that all people of color are inferior to white people and therefore should be exterminated for the good of humanity. The opinion itself, technically, TECHNICALLY, isn't harmful. But that means nothing, because opinions always lead to and/or inform action.
Everything you do is based on a collection of opinions. You chose or ended up in the job you're currently working due to a mix of opinions on what kind of work is good and/or fun and/or profitable and/or worth your time, plus many other factors. I attend protests due to a (fact-informed) OPINION that we're on a fast-track to mutually-assured destruction and if nothing else I at least want to be able to look back from the rubble at say "well at least I did SOMETHING."
Let's take some sample opinions and follow them through likely actions and consequences.
Opinion #1: "Cookie dough ice cream is the best flavor of ice cream."
Likely action: Buying more cookie dough ice cream than other flavors.
Likely consequence: Sales of cookie dough ice cream increase slightly.
Is this a harmful opinion? No, because the actions and consequences of those actions are not harmful. This is an example of something that is truly "just an opinion" and if I were to call you a bad person for holding that position, I would be an asshole. Now, let's introduce a similar opinion.
Opinion #2: "The ice cream company Dreyer's makes the best ice cream."
Likely action: Buying more ice cream from Dreyer's than from other brands.
Likely consequence: Dreyer's profits increase slightly.
This still seems like a harmless opinion, and very well could be. But what if Dreyer's makes its ice cream with a special ingredient only found in Peru, and the company gets it cheap by enslaving Peruvian children, bulldozing Peruvian villages, and murdering and Peruvian people who get in the way. At this point, buying Dreyer's ice cream could be funding a horrifying Peruvian genocide.
But of course, it's not that simple. People don't hold just one opinion at a time. Your decision on whether to buy blood ice cream will be affected by other key opinions. Consider this:
Opinion #3: "My ice cream preferences are more important than the lives of humans I never have to see."
Likely action: Continuing to buy Dreyer's ice cream.
Likely consequence: Dreyer's continues to murder Peruvians to meet the demand of their customers.
Now let's consider a real-world situation (since no, Dreyer's is not murdering or enslaving Peruvians to make their ice cream, sorry Dreyer's):
Opinion #4: "Donald Trump would make a good president."
Likely action: Voting for Donald Trump.
Likely consequence: Slightly increased chance of Donald Trump becoming president.
What are the consequences of Donald Trump becoming president? Validation of serial sexual assault as an acceptable behavior, validation of racist and nationalist attitudes, legislation that increases Islamophobia, leads to more refugee suffering and death, increased deportations (leading to death, increased poverty, broken families), increased homophobia and transphobia, withdrawal of funds from programs that feed the poor, children, and elderly, withdrawal from the Paris Climate Agreement, leading to an increased chance of climate change spiraling out of control, leading to the destruction of human civilization and possibly the entire species.
Wow, that is a lot of harm! Even if climate change doesn't kill us all, people have already been harmed on a massive scale by Donald Trump's presidency. Even just electing him led to a validation of other very harmful opinions that have led directly to deadly hate crimes. I've yet to see any evidence that electing Trump has resulted in less harm for anybody. And rich people getting tax cuts doesn't count because those people are not harmed by taxes. They are not in danger of starving or dying from preventable illness like the rest of us are.
And yes, you could argue that liberal or leftist opinions could lead to harm. You could easily argue that and if you're pissed at me right now I'm sure you're already doing it in your head. But that is not the point of this post. The point is that opinions are not neutral. They are not all the same. Some opinions are virtually harmless, while others are very harmful, because opinions lead to actions that lead to consequences. You act on your opinions a thousand times per day. So it is my opinion that you should shut up with this "just an opinion" nonsense and join the rest of us here in reality.
And remember, there is a stark difference between "opinions" and "facts." Don't be like this individual:
Facts are like assholes. Everyone has one.— illiberal (@Illiberalality) July 3, 2017