I agree in not allowing babies, especially newborns, to be left crying with no response.
I have done both though.
When my first was born I had a combination of undiagnosed reflux, a mother and grandmother with a victorian attitude to bringing up children and only one friend had had a baby and she handed me the Gina Ford book as soon as I announced my PG.
Unfortunately I had DS 3.1 weeks early and he had reflux. I had never heard of it and I was constantly at the doctors explaining that he wouldn't stop screaming and I struggled to BF him, he kept arching and pulling away
. The useless Docs and HV didn't mention reflux, just said it was 'normal'.
I was an absolute state of anxiety and nerves and my mum said "if he's been fed, burped and changed and he is still crying there's nothing you can do except allow him to cry it out.
I actually used to bury my head under a pillow and cry, listening to him scream and scream as cuddling him didn't work and my mum put the fear of god into me about letting him sleep in the bed or on DH. I thought id suffocate him.
He was 5 months old before I took him up to hospital and broke down and the Doc diagnosed reflux, gave him meds and he turned into a happy baby.
DD was also born 3.1 weeks early (I have an impatient womb
and she had reflux but I knew what it was by 5-7 weeks.
She slept on DH or me for 3 months and we literally walked around with her for 5 months.
The difference was,I now had the experience of talking to other mums. I felt awful and I worried myself sick about what I might have done to DS.
Like your friends, it was a case of I just didn't know better.
I think people can be very judgemental especially when it comes to bringing up children.
I don't think many parents will set out to damage their children. They just might have different ideas from different sources.
DS is a very confident happy little boy but (now 3.5) but Ive noticed when he is very upset (maybe been woken up or had a bad fall)he is hysterical and can't be comforted easily until he calms down 

.
I obviously blame the crying at an early age but I could never be sure.
DD however (now nrly 11 months) will stop crying when picked up.
Maybe your friends could do with some gentle advice but it's a tricky one.
I would have appreciated it but not sure how id have taken it if it seemed like a personal attack, tread carefully.
Just out of interest, They both didn't sleep through until 6 months so it didn't make a difference that way.
I never starved him through the night though, Id always make sure he wasn't hungry first - shudder at the thought of starving them
.