M.P.
I suggest that this is just a stage in his development and he will learn how to soothe himself. I suggest that letting him cry it out only makes it harder for him to get to sleep. He gets rightfully upset and can't calm himself down.
I suggest that you not immediately go in to him but once his fussing becomes crying that you go in, check to see if he needs a dry diaper, more covers, less covers, etc. Then without picking him up, gently pat him for a few minutes before leaving. When he starts up crying again, repeat the patting and leave. Eventually he'll learn that you're there and will take care of him but that you're not going to pick him up.
He may be going thru a growth spurt and need to be fed. Or you might try giving him more to eat/drink just before he goes to sleep at night. When you fed him did he eat like he was hungry? If so, feed him that first time going in to him. Then just go in, pat him a bit and leave. He will learn from repetition, what to expect. He will also learn how to soothe himself when he realizes that you're there every 5-10 minutes.
It's suggested you go in after 5 minutes a couple of times and then gradually extend the length of time before going in to him.
One reason I believe cry it out isn't healthy for the baby is that their nervous system and understanding of emotions isn't such that they can soothe themselves once they've worked themselves up into a frustrated cry. When they do learn to not cry they've stopped because they realize crying doesn't help them and they feel helpless and hopeless. They've learned a negative about life. Someone won't always help me. I'm on my own even tho I'm a baby and can't help myself. This builds just a bit of distrust that when combined with other experiences can teach a baby and then child to learn not to trust their world.