I saw this question so often around the forum and club in general, I wanted to give my answer. I’ve been firmly Captain Swan since the bean-stalk, so keep that in mind while I point out all of Hook’s shortcomings.

I believe there are many reason to this dislike of Hook.
When Mary Margaret and Emma first met Hook, he was working with a woman who had just murdered an entire village, lied to their faces and was planning to double cross them. Snow knew him by reputation as a ruthless pirate captain, and repeatedly told her daughter not to trust him. He later ripped the heart out of Aurora to...

Tallahassee

"I was hoping it'd be you."
"Don't think I'm taking my eyes off you for a second." "I would despair if you did."
"You know, most men would take your silence as off-putting, but I love a challenge."
"You're something of an open book."
Killian recognising Emma's lost look.
"Love's been all too rare in your life, hasn't it? Have you ever even been in love?"
Killian bandaging Emma's hand with his scarf and tying it with his teeth.
"I'm always a gentleman."
Emma noticing Killian's Milah tattoo and realising that he lost more than his hand to Rumplestilskin.
"For someone who's never been in love,...