Most Helpful Guy
After sex, the basic male biological imperative is to protect and care for family.
Almost all males think they are better than any other male at protecting a family - in particular, his family.
A man's daughter is not just his family, of course, but is his personal biological investment in the future of our species, so it is something extremely important to us. In particular, females over males because, physically, males are more capable of taking care of themselves and protecting the social clan - killing dinner and killing predators that would otherwise kill us and killing competitors from hostile clans. Females biological roles are making the next generation and being the essential glue in the social clan. (Yes, this is all very sexist, but Nature doesn't give a rat's ass about political correctness.) Also, since males can squirt with impunity, a man's genetic investment in the species is more easily spread via his sons. Not so with his daughters who can only bear so many children...
So, basically, a man has a shitload invested in his daughters. He'd rather care and protect them until he is dead.
At the same time, he realizes that he must "let her go" and find love and be with another man to start their own family. No generation is special and the passing of torches between generations is the natural order of things.
Thus, a father realizes the daughter will have boyfriends, but the father wants to make sure that the boyfriend is 1) "worthy" of his daughter and 2) capable of replacing the father in caring for and protecting his daughter. In a man's eyes, almost no other man is adequate to the task...
Also, like others have said, we remember what it's like to be a young male and, being older, we also realize how much young women don't understand young men very well and how powerful our sexual instincts are. Also, being older, we also now are fully aware of the strength of female sexual instincts. So, we are vigilant and concerned about our daughters "getting into trouble" ruining their lives because of a douchebag boyfriend and, also, implicitly, ruining the man's biological / genetic investment in our species.
So, when you put it all together, we get the impression that "Fathers hate daughter's boyfriends." The fathers don't actually hate the boyfriend, but they will hold that boyfriend to a very high standard. A successful boyfriend will be smart enough to know this and act accordingly.2
Most Helpful Girl
My dad is literally cool as shit, he's all jokes. Mind you it's tradition that he'll threaten to kill my boyfriends if they break my heart but he always follows it with a backslap and a laugh.
Besides he wouldn't kill em'. Maybe break his legs but shit he's a civilized man.1