@Krillin:
Franky started out theatrically Evil with his mask and big debut on top of the arch in Water 7.
This isn't what cartoonishly evil is. Franky may have started out as a petty thief, but we were eventually exposed to his true character shortly after.
Please tell me how Franky robbing somebody and then attacking them is the same as a sadistic scientist who develops weapons of mass destruction to destroy countries, and who develops poisonous candy in order to test it on kids to create human weapons.
and getting new crew members doesn't have established people join because they've been pressured into leaving (Sanji and again Franky falls into this category), people invited by luffy solely because he likes them (Usopp, and Jinbei).
Uh, yes it does? They're introduced at the beginning of their respective arcs with a unique defining design and personality, the entire crew interacts with them in some way, Luffy is shown to like them, their backstory is hinted, and then later established in a flashback. Then, they participate in the final battle against the antagonist, get several character defining moments during that final battle, and then by the end, they decide to join.
That's the barebones of the pattern, without taking into account the exact specifics.
We've had people people recruited because of strength (zoro)
Zoro wasn't recruited just because of his strength. Luffy and Coby went to the Marine base because Luffy was interested in him, but it all boiled down to Luffy liking him, and him having an actual reason to travel with the Straw Hats (a dream).
people just tagging along I.e Nami
We were given a hint into Nami's past before the fight with Buggy, and she participated in the brawl against the Buggy Pirates.
In the end, Luffy liked her, she had the navigator role, and she was a clearly defined character that had a reason to travel with the crew (which would later be expanded on and lead to her official joining)
people request to join (Robin)
Robin is the only curveball exception to the pattern. Even then, Luffy liked her during Alabasta, and we had a small peek into her motives/dreams when the poneglyph was encountered.
people join out of role necessity, (Franky, Chopper)
And both of them also joined because they had established dreams, along with interactions and chemistry with the crew. If it was all about "role necessity" instead of actual character, some random shipwright from Foxy's crew would've been picked up.
people join because they've been pressured into leaving (Sanji and again Franky falls into this category)
This is part of something that happens with most of the crewmembers. While the circumstances are different, most of the Straw Hats have had emotional farewells with their friends or families as they sail off or just before they leave (Nami with the Cocoyashi Village citizens, Luffy with the Foosha Village citizens, Usopp with Kaya/the three children, Sanji and Zeff/the other chefs, Chopper and Kureha, Franky and the Franky Family, and even Brook, who had a funeral for his lost comrades at the end of the Thriller Bark Arc).
Ultimately, Sanji and Franky joined because of their uniqueness and setup as main characters.
Then theres the Luffy thinks amazing category (Brook)
But also because Luffy liked him, because of his unique character design/personality, because of his ample screentime during his introduction arc, because of his role as a musician, and his dream that required/motivated him to travel with the Straw Hats.