While I have no problem with warlocks being based on pacts, I would like to have the option to play a warlock whose ancestor made the pact, or who was marked by some supernatural force without his consent, cursed by a fey while in the crib, etc. I also think it's very important that warlocks, no matter what the nature of their pact, are not beholden to their patrons once the pact has been forged. If I wanted to be the devoted servant of some higher power, I'd play a cleric or paladin. Warlocks, IMO, should be those who make dangerous bargains with strange otherworldly beings, scholars who seek out terrible and forbidden secrets that would drive lesser minds mad, and cunning arcanists who pry into the cracks in the universe that the gods had thought they had safely sealed away.
Warlocks should rightly be feared, and should be able to turn against the very beings that were foolish enough to curse them with their power. They shouldn't be portrayed as gullible fools who were too incompetent to be a "real" wizard so they sold their soul away for whatever scraps of power they can beg out of some greater being. Why would anyone want to play that? I want to play a warlock that other people fear and respect because he's powerful and cunning enough to delve into dark secrets that most people don't dare touch, not someone deserving of pity because he was so pathetic that they only way he could get power was to go begging for it.
A wizard should talk about his warlock friend like this: "That guy? He's a warlock. In my pursuit of knowledge, I myself have often felt the temptation to go to the dark side, to delve into those secrets and to commune with those beings that the gods tried to keep locked away - and for good reason. Many who gain such insights go mad. But a true warlock is one who is strong enough of mind and soul to not only unlock such forbidden insights, but to master them. He is cunning enough to bargain with arch devils and arch fey and come out ahead. He is willing to do almost anything for power, no matter the perils. It is fair to say that I regard him with wary respect, and even a healthy dose of fear."
Not: "Oh that guy? He's a warlock. LOL. He didn't have what it took to be a real magician, so he sold the only thing he had that was of any value - his soul. What a noob."