Can you give an example of someone in a modern democracy jailed for their "opinion"?
To wit, are the examples you're thinking of "statement of opinion", "statement of fact", "pejorative insult", or "incitement"?
Saying "I think <public figure> is an idiot" is an opinion. "The earth is flat" or "The holocaust never happened" are not opinions; neither is, "Kick out all the <insert pejorative here>."
And yeah, in North Korea you'll absolutely be jailed for expressing some opinions. That may make them illegal, but it doesn't make them no longer opinions.