It did not appear to be unserious in context. It appeared to be perfectly serious. And the person to whom you were replying was almost surely serious. They were using a string of escalating incentives (which, yes, became quite extreme!) to show the point that on most things--not absolutely everything, but definitely most things--"utterly and eternally unwilling to be persuaded/intimidated no matter what" is ridiculous and inaccurate.
Their whole point was to show you that what you almost certainly actually meant was "unwilling to be persuaded, except by means which the party would find too extreme/evil/difficult to actually do", outside of a small handful of exceptions.
And I'm only beating on this dead horse because people kept, over and over and over and over, pushing back that no, this is totally realistic, how could you possibly think this was in any way weird or problematic? If you meant it unseriously, the thread at large definitely didn't take it that way! It's not JUST me thinking that.