Oh man, I understand how that happens… like TONS of people ship Dean and Sam together on the tv show Supernatural. (Castiel all the way tho, guys, like come on. What what what are you doing.)
Personally I don’t think I will ever be on board with ships that are between siblings. But I think if you wanna ship Frank and Joe just for fun in your head, it’s cool. I’m not gonna stop you. They are fictional characters and everyone is entitled to their opinion. The only times I don’t think it’s okay to ship something is when it genuinely sends out a bad message to people.
For example, another common ship trope that I really dislike is teacher/student relationships. (Or any sort of adult/child thing… no thanks.) I think that it promotes unhealthy relationships and it’s really not okay to perpetuate. (One major thing that comes to mind is the tv show Pretty Little Liars where it makes a relationship between a sixteen year old girl and her high school teacher seem plausible and normal and THAT IS NOT OKAY. Especially considering a huge chunk of the audience of that show is in high school.)
Oh and another thing is that I will never ever ship something that is non-consensual and/or abusive and I WILL judge the fuck out of you if you do. Under every circumstance. Cause that is absolutely not okay with me.