There are many good, dependable knives with liner locks. It's just that I don't particularly care for them. With so many knives to choose from, anyone can get any kind of knife one wants. I simply choose to buy knives that have, in my mind, better locking systems.
Liner locks cost less money to produce, so it's a great way for a manufacturer to keep the cost down and the profits up. Boker produces many liner lock knives and they put out a decent product. And in my opinion, liner locks are a hell of a lot better than slipjoints.
Any liner lock can fail if stressed and there are better locks on the market. It's just like bikes. There's nothing wrong with a 3-speed bike, but why get one when you can get one with more gears for the same price?
I prefer frame locks, lockbacks and axis locks, all of which I believe are superior to liner locks. So when I see a liner lock, I just keep looking until I find a knife with a different lock. If someone gives you a liner lock, there's no reason to get rid of it, but if you're buying for yourself, there's no reason to get one.