"If you don't have something nice to say, say nothing at all."
I'm so glad I never grew up with that saying. I grew up in a family that was honest. Honesty to the max. If there was something nice to say it was said. If there was something bad to say it was said as well. There was no holding back with praise and blame.
Also I learned the difference between mindless criticism and constructive criticism. And I'm happy to actually see a difference, because I noticed that people who did not grow up in an honest family have trouble telling both things apart.
To them any criticism is an act of disrespecting the person. And truth be told it often comes across as such. But constructive criticism rarely is disrespectful to the person, but to the thing that is being criticised. That may be a behavior, a thing they said or did or some other stupid thing that happened to the person. Naturally the person will be mentioned within the context. And so it can very easily be confused with disrespecting the person him-/herself.
I give an example of a similar thing. And it's even magic related. Some people don't like magic. They somehow don't see the magic as an attack of their logic, but as an attack on themselves. The subtext they read into a magic performance goes like this: "I don't understand how the magician does this, ergo I'm stupid."
We magicians know that this is really not what is going on. Yet those spectators see it as such.
Same with criticism. Some simply see any criticism as an attack on themselves, rather then seeing in as an attack on the argument that is being criticised. And that has something to do with having been raised with questionable moral advice.
Advice like: "If you don't have something nice to say, say nothing at all."
"If you have something to say, say it, and back it up with arguments."
"Don't be afraid to be wrong. If you are wrong, admit defeat and question your arguments."
"You don't have to be right all the time."
"Before taking advice, see where the advise is coming from!"