D.S.
I am sure it is just habit at this point. It really is personal preference if you want to allow co-sleeping. I personally never did it because my husband is 315 lbs and 6'3 I was so afraid he would roll over on my kids I never felt comfortable. If it doesn't bother you then let him in if it does then I suggest you get a gate and when he calls for you just go in and put him back in his bed. When my kids had nightmares or were not feeling well I would always go to them and sit beside them on their bed rub their back until they fell back to sleep. I would never get into bed with them and they did not come in my bed. I felt as long as I was close enough to them to comfort them I didn't want to start bad sleeping habits. In reference to children being ripped from their beds and murdered I do think that is an extreme situation. On the flip side of that infant mortality has tripled in the past twenty years due to co-sleeping from suffocation, or strangulation and that is a fact from a recent government study. I must say I think the risk of death or injury is higher in co-sleeping then the chance of someone abducting your child from their bed. Like I said this is personal preference and basically what works for your family. But for now if it is bothering you then you may have to suck up a few nights of no sleep and walk him back to his bed within a few nights of doing this he should stop waking up.
Good luck!!!