I think that is what the bribe stuff is about. Apparently as you stated getting to diamond gets you the 4 free drinks per day. Since Carnival doesn’t offer anything like that in their loyalty program the poster considers that a bribe.
I am one point short of Diamond myself with Royal. WhenI get there I get there. 😀 not much of a drinker so the “bribe” doesn’t really sway me. Their ships sway me just like the Vista and excel class ships got me to come back to CCL.