The original concept of attachment was a psychological theory developed in large part by two researchers, John Bowlby and Mary Ainsworth, in the 1960's. Ainsworth classified mother-baby dyads into three categories of attachment based on observations of the infant: secure attachment, anxious-resistant insecure attachment, and anxious-avoidant insecure attachment. Infants who had a secure attachment to their mothers were able to better explore their environment, play and learn.
Today's "attachment parenting" is much different. Largely pioneered by William Sears, the attachment parenting style does encourage breastfeeding, babywearing, and cosleeping. The real ideas behind those specific behaviors are what separate attachment parenting from other parenting philosophies. Attachment parenting asks that parents of infants see parenting as a mostly child-directed activity. Therefore, you should respond to your child's needs, rather than forcing your child to conform to your schedule. E.g. breastfeed on demand, rather than by the clock, and respond to baby's cries by picking her up, even in the middle of the night when she refuses go back in her crib.
In constrast, other parenting styles, such as Babywise, take a more parent-directed, or both child and parent-directed approach. They believe that setting a flexible feeding schedule for your baby helps him to gain a comforting sense of structure, and that allowing a baby to cry in his bed for a short period of time isn't a bad thing because he will learn to fall asleep by himself and won't be dependent on someone's arms to put him to bed. These kinds of parenting styles are much more common in the U.S., where we have a higher value on independence, even for infants.
The ideas (like breastfeeding, babywearing, cosleeping) behind the attachment parenting strategy are really fairly well supported by the scientific literature (Yes, there is scientific literature on these topics. Whole journals, in fact.). However, I do not think there is evidence to suggest that a child reared using a different parenting strategy is any less likely to be securely attached, at least the way researchers think about attachment.
If I were to offer a criticism of attachment parenting, I would say it perhaps requires more of parents than is reasonable for the average family, and is a bit too rigid for specific kinds of families. Parents should not be made to feel guilty if they must give up breastfeeding to earn an income, and parents from varying cultures should not feel they must replace their traditional childrearing styles to conform to attachment parenting beliefs. Additionally, there are individual differences between babies and certain parenting behaviors may work much better for one baby than for another. I believe in a more balanced approach to parenting, and I encourage you to do some research, try some different things, and ultimately pick and choose which parenting strategies work best for you and your family. You don't need to have a "philosophy" about parenting in order to be a good parent.