My parents slept with me in their bed until I was 5. It warms my heart to remember snuggling up to them at night. Even though my teenage years were really rough and my parents and I struggled, I never forgot how they snuggled and loved me, and always knew that I was loved.
I have co-slept with all three of my children, one of whom is now a teen. I would NEVER call it a mistake.
I do realize that a young child in the bed can be a challenge at times, especially when you want some "alone time" with your husband or when your little one is tossing and turning. May I recommend a co-sleeper? These are sort of like cribs with one side missing. It straps to the side of your bed, allowing you to cuddle (and even nurse, if you choose!) your little one without them being actually *in* the bed with you.
PLEASE: try to imagine how your child feels. They want to sleep in your bed because of the warm, loving feeling it gives them. They cry when you take them out of your bed because it leaves them isolated, without your warmth and your reassurance. They cry. When they are old enough to face the night alone, they won't mind moving out of your bed, but until then, they prefer to know that you are there. I think kicking them out of your bed and letting them cry it out is cruel, and sends the wrong message to your child.