It's not about a code of conduct, but moreso the mind set. Paladins strike me as laser beams. Focused on expanding the pantheon of their deity. They do it through their actions, and generally their actions involve combat. When they are not fighting, they are training, or worshipping. That's it. It's possible that they have sex, but the discussion was regarding prostitution. Would a paladin have sex for coin? Taking into account that in the "realms", prostitution might very well not be a big deal, but does a paladin have TIME for it? They're busy. Unlike the other classes that are generally focused on one aspect that takes up their time. Warriors train, and then have sex. Thieves sneak around and then have sex. Clerics worship their deity and then have sex. Bards are gay and then have sex...Paladins have training, THEN worship their deity, and then have sex. They have one more responsibility that the other classes don't.
Clerics are the the ones that have a number of different roles in the "D&D clergy". They are the ones that have the time and opportunity to divide their interests in a number of different ways; sex being one of those ways.
I suppose I'm still old school D&D where Paladins smashed more, and Clerics were the jack of all trades, and masters of none types. Even moreso than bards because bards are just gay. :) You can throw jongleur, and blade kits at me till the cows come home...bards are teh g4y.
When 2nd edition rolled out Clerics became a bit broken. There were two clerics in our party and they became a huge obstacle for our DM at the time, simply because of the spells that they had available to them. The party pounded through fights that we never should have attempted, solely because of the spell set of the clerics we had in our party.
Where was I?
Oh...like I said earlier. Have fun with your paladin orgy...seriously...please do. Something inside me kinda snaps when people try to actually justify outlandish ideas. Embrace the outlandish.
Have a three peckered paladin having a threesome with a ghostly japanese school girl and a tentacle god. Have five cat girls cheerleading on the side.
Just don't try to rationalize it.