General

So It’s almost impossible to find a relationship with someone who’s into this detail. I don’t think it’s wrong to feed someone and have them gain weight if they are into this fetish’s because they would be miserable being thin.

Do u think it’s wrong or immoral to be in a relationship with someone and have them gain weight if they aren’t a feedee but just a normal person who consented. Like they could be in a relationship that would be healthier as the alternative.

Not at all. Some thin people might prefer to be heavier even if it isn't a fetish

No harm in asking I suppose they can say no if they don't want to do something like that.
I asked a BF to gain for me and while he did gain 15 - 20 lbs but he didn't care for the feeling and lost the weight.

The only way it's immoral to ask is if you know you're into this stuff going into the relationship, it's a deal breaker (like you know you won't be happy without feeding/fattening), and you wait UNTIL it becomes a relationship before bringing it up. Then it becomes emotional blackmail unless you make it clear that you're solidly willing to take no for an answer. An exception would be if they don't know anything about feederism, clearly like overeating, have no problem eating in front of you, and make it clear they are happy at any weight or are unconcerned about weight gain. But if you're into immobility or a death feedist, you have to be willing to accept a hard no whenever you decide to bring that up (maybe not let all your crazy out at once.)

Secretly enabling and sabotaging a food addict who easily gains weight and is too enamored with you or too submissive to stop until they're so helpless that it's too late, reminding them constantly that it's their own fault as every pound brings them closer to the grave is HOT fiction... but rather uncouth IRL.

Your right about the partners health an also about power comes great responsibility.