I can't see how you'd do it without being preachy.
Oh, that's easy. For example:
Option 1Create a first person view nightmare simulator where you're the pig and your task is to escape the slaughterhouse. Include vivid, graphic depictions of animals being slaughtered. Every time you fail and are caught, show yourself being slaughtered with copious amounts of blood. Bonus points for making it VR compatible.
Have no narration, no preaching, no taglines...nothing. Simply show the scenario for what it is, with you in the role of the pig.
Option 2Same as before, except all of option 1 is exclusively act 2 of the game. Act one takes places on a farm house and is a a first person RPG with dialogue between you and the other farm animals. Include multiple romance options and make it kind of like a dating sim, with several cute pig girls to choose from. Show them very happy and make the animals all kind and nice and lovable. Show
nothing to do with humans. No mean ranch hands, nothing. Act one is exclusively to establish emotional rapport with the characters.
Then introduce act 2 as what happens when you're taken to slaughter. End act 2 with the horrific realization that the friends and lovers you had during act 1 didn't make it out.
Option 3Put the player in the role of the slaughterhouse owner. Portray the animals as affectionate and loving. Balance the game such that being kind to the animals is cost ineffective, so to succeed you have to "cut corners." Where cutting corners means forcing animals into cramped cages, not using anaesthetics, not giving them proper medication, feeding them the corpses of their fallen, etc. Graphically show the consequences of the actions the player chooses to take. Occasionally have disgruntled employees abusing animals. Have there be no in-game consequence for allowing it. Allow players to choose to be the bad guy, allow them to play the bad guy, and apply absolutely no judgement of their actions. Only show the results, and let them come to their own conclusions.
Option 4Do what
I have Candy Get in the Van did. Put the player in the role of
potential bad guy, but give them no prompting as to how they should behave. However, put in achievements and different game endings for different play styles. Make use of compulsive 'I have to unlock everything!' gamer behavior to allow players to convince themselves to do things they would ordinarily never choose to do. Offer absolutely no moral judgement, no preaching, nothing regardleses of what the player chooses. Simply put the player in the position of getting to decide what to do and then seeing the consequences of it. For example, make it possible to build a sunshine and rainbows ranch where no animal is ever killed and only given hugs and pretty ribbons for their hair and money is made exclusively from non-lethal things like shearing wool during summer. Have an ending achievement for that kind of gameplay, but provide no preaching to say that it's the correct playstyle. Simply allow it as a valid playstyle and allow the player to choose or reject it.
But design the game to allow every possible sort of ranch, each of varying levels of cruelty, and keep showing them those missing achievements, so that the completionist streak compels them to play the darker, more sinister playstyles. And as above, offer no values judgement of their choices. Simply allow the player to choose, and show the consequences of his actions. Even if that means letting them be the bad guy and getting away with it and letting them
win. Done well, this can be far more deeply horrifying than a more direct approach.
Lots of ways to effectively communicate the message without being preachy.
But you
don't do it by making a silly little 2d platformer where 90% of gameplay is jumping on floating things trying to evade rancher sprites, with industry fact text blurbs as your end of level rewards.