I don't think they are harmful.  Unless there are small pieces that come with it or can break off and accidentally swallow!!!  In my opinion, I think it teaches them empathy, esp. around age 2-5.  They have to care for another "person," which is the baby doll.  There's some debate over whether dolls make kids want to have kids (teen pregnancies) but I don't put any stock into that!  I played with dolls as a baby and as a child, and I still don't have kids at 37 yrs of age! 

i see, so psychologically its fine right?

see sometimes a doll makes a baby/ kid cry for some reason

Yeah, sometimes maybe they are scared because they are confused.  If they are really young, like, an infant, their vision is still forming, so things are blurry, and they feel comforted only by the blurry face of Mommy!  If they are a bit older, like 2-3, maybe the realistic look is kind of scary, they think the doll is real, and they might be in that "stranger anxiety" phase of development...like, "who is this weird little person next to me...aaahhhh!  Where's my familiar peeps?  Mommy!!!"