All cops deserve to die. Also “pig” is a fatphobic insult that criticizes cops more for their weight than for the fact that they are enforcing oppression. Most fat people have experience being called “pig” as an insult for the fact that we are fat so when we see someone do it to others, no matter how bad they are, we assume that it is because of their weight. Fat people and pigs deserve to live while cops deserve to die. Saying this as a fat brown disabled person who has experienced being abused by cops.
I understand how your experiences must make you quite averse to the term, but unfortunately that's not fully true. The term was used for police officers as early as 1811 in England's London (source, source, source). There are different theories on why the term was used, some believing it's linked to the term "nose" that was also used at the time for sniffing out crime. Some believe that the term was used to invoke the idea of being greedy, hoarding wealth.
The term regained popularity in america in the late 1900s. I'd invite you to read this speech by Bobby Seale who was chairman of the Black Panther movement at the time. I can highlight the main anecdote, which is about a man trying to get clean water but cannot find any. He finds another man who "says "there's a hog in the spring." He says "there's a hog in the spring, and a lot of those pigs are running around too in the spring." All we want is a little freedom, all we want is a clear drink of water, but there's a hog in the spring!
Look, how should we try and how should we work to get the hog out of the spring? Now the spring has been running dirty for a long long time for peoples in Vietnam, for peoples in Africa, our black brothers, for our black brothers and colored brothers and sisters in South America and Asia and the Caribbeans etc., throughout this world.
Where three-quarters of the world who are non-white who've been brutalized and beaten and exploited and colonialized etc., by this racist power structure here in America. The hog has got to be removed from the spring."
The main comparison to being a pig here is the association with filth and the idea that they pollute the surroundings for everyone else with their presence. Seale goes on to call them "Pigs. Hungry, exploiting, robbing, thuggish pigs. A whole power structure and all its racism." Further comparisons highlight them (the police, which he is calling pigs) as a source of incredible violence.
I don't want to throw too many sources at you but I'd like to note that animal epithets have been used since antiquity. Comparing people to swine has long been used as an insult. And I agree with you, actually, that some of those uses are fatphobic in nature. Pigs are fat so they call fat people pigs. But "pig" is not an insult because the animal is fat, it's because they're seen as filthy or greedy; the term hogging is a clear example of this. Or the way we compare dirty living spaces to a hovel. When people use "pig" to insult fat people they are being fatphobic by dehumanising people, and by playing into the fatphobic idea that people who are overweight are only overweight because they're greedy and insatiable. (There's too much to deconstruct with that assumption.) However the insult "pig" for police was not originally fatphobic, and was used for a long time for reasons more than just the idea that the police are fat, which is I think more of a stereotype in the US - I'm not overly familiar with it. I don't think you have to like the term. I don't think you have to use it. But I don't think it's fair to say it's only fatphobic when, historically, it hasn't been.