Wikipedia defines common sense as “knowledge, judgement, and taste which is more or less universal and which is held more or less without reflection or argument”
Try to avoid using this topic to express niche or unpopular opinions (they’re a dime a dozen) but instead consider provable intuitive facts.
When people say that, they mean they’re so much smarter than everyone else they could fix it all in a moment.
Of course, in reality, the cranky old man saying that has just stayed so uninformed about the issues he doesn’t know what he doesn’t know.