conjunctions - Where is the line drawn with comma splices?

I was going to ask: where is the line drawn between parentheticals and comma splices?

I've been trying to think of examples, and all the ones I've thought of seem okay, but probably work in a third way again.

"He didn't hate sailing, he loathed it."

"He hated sailing, he was always seasick."

"He disliked sailing, he wasn't good at it."

"John dislikes sailing, Mary dislikes sport of all kinds."

None of these seem like genuine parentheticals, they seem more like subordinate clauses with the subordinating conjunction left out (if that is even a meaningful distinction). But they also seem like common literary AND conversational constructions, even if they are considered wrong.

Are there loopholes whereby what appear to be separate independent clauses can be joined without a conjunction?