Alright so now regarding why diaperfags like pacifiers. Now interstingly enough this is something that can and is enjoyed by non-diaperfags too. It has to do with the sucking motion.
Now at birth a preset reflex for all humans (and almost all mammals for that matter) is the sucking reflex. Now the way the primitive brain works is that when you do a proper action your brain rewards you will some endorphines to positively reinforce the behavior. So when a baby sucks the brain is flooded with endorphines and in a sense they get a mild high.
This particular reflex is a protective reflex where once a baby is placed on their mother's teat they would begin to suckle allowing milk to flow out letting them feed. It is also why giving a pacifier to a baby can sooth them, when they suck their brain is rewarded endorphines and the amygdala (emotional center of the brain) is suppressed.
Now as you get older this reflex (much like the babinsky reflex that allows babies to brace themselves with their legs when their feet touch the ground) dissapears. However that same reward pathway is still active. So though the act of sucking you get a minor high. This high isnt remotely close to the high provided by eating or sex, but through its slow long release time it tends to have a soothing effect instead of a high effect, and your emotions are more easily regulated in the brain due to supression of the amygdala from being overactive for a longer period of time allowing your hippocampus to deal with them for a longer period of time.
Now while this is all true, the question is, what would drive someone to start sucking as an adult in the first place. That is where >>15608
hit it right on the head. Oral Fixation is something that was first brought up by Sigmund Freud in his concepts of delayed stages of development. (I know people dont like him for being mean, but bear with me)
If we go a bit further into detail during the first 2 or so years of development you are in the Oral stage, where you desire instant gratification. Now to complete this stage the concept delayed gratification must be learned (where it is better to delay getting something you want, for a far better reward later). Now when you neglect a child during this stage they may end up independent but left desiring that oral stimulation later in life they were denied, however if you overprotect a child during this stage they might end up depended on others to provide stimulation and as a result resist maturing.
Now oral fixation manifests in a few ways such as smoking, chewing things like gum, excessive drinking, and excessive eating. In a sense a lot of people that think they need to smoke for the nicotine, actually just have an oral fixation, as >>15488 noted in a decreased need to smoke.
Hmm so in a sense any human will find the act of sucking enjoyable, the only exception I can find is if the individual has taken enough drugs (cocaine, meth, etc.) to permanently alter their bodies reward system to where the minor high is no longer effective due to their brain needing more endorphins to get that high). But that that point they probably don't get the same high from eating either.
So yeah I think that is about it, the reason for liking plushies and snuggling them also has a similar method of activation but that one is dependent on Oxytocin and has its own separate long story filled with experiments.