Considering how nearly all of Europe didn't know that North America even existed for most of the last 2000 years, I find it hard to imagine how any idea would be able to be conveyed around the globe. Today, that can happen in minutes. While you are correct in assuming that I am no historical scholar, this still seems like a significant difference to me.
Let's imagine your bad idea was posted online in English. In China, it would only be accessible by "fewer than 10 million Chinese, or less than 1% of the population, [who speak conversational] English."
[1] Before Europeans dabbled in America, there were only between 50-100 million Native Americans.
[2]This means that today there would be roughly 1.4 billion people in China alone who would likely not be able to access the original English. Now imagine if the bad idea was a tweet in Irish...
So yes, an idea
could be spread across the globe in minutes (assuming everyone had access to the internet/smartphones, which is itself a problematic assumption). But there are certain natural barriers to comprehension and understanding, whether linguistic or even cultural. A tweet saying 'relax, dude' from a Californian would be interpreted in a vastly different way from its intent by, say, a Tibetan monk.
Arguably, from ancient times until even the 1800s it may have been easier to convey ideas. The educated elite who wrote letters, treatises, pamphlets, books etc. almost exclusively wrote in or understood either Latin/Greek throughout Europe and the Middle East. Granted, it wouldn't take minutes to get from Ireland to Istanbul. But once it did, it would be fully understood, copied, talked about, (and possibly declared heretical, hah).
To conclude: ye olde communication might have more steps than it does today. But it still allowed one person to shake the world.
[3][1]https://www.chinahighlights.com/travelguide/english-levels-in-china.htm[2]https://en.wikipedia.org/wiki/Population_history_of_the_Indigenous_peoples_of_the_Americas#:~:text=Population%20figures%20for%20the%20Indigenous,of%20100%20million%20or%20more.
[3] Or, at least, the subsection of the world capable of receiving, understanding, and caring about the message.