I know that's probably considered an unpopular opinion today, but I actually like the idea of constructive criticism in fandom. Particularly in fics.
There are so many people that get mad about the idea of someone leaving a potentially helpful tip or two in the comments of a fic, and I don't really understand why.
"BuT tHe cREator DiDn't aSK FoR It!! Fandom is supposed to be a safe space!!1!"
First off, by no means is the internet a safe space, but I digress.
Let's say that you have one of those relatively common cases of young writers who are just now beginning to write fanfiction and they tend to clog an overly long text in a single paragraph. It's in no way harmful for someone to leave a comment saying, for example: "I like how you did X and Y but please consider separating paragraphs more often".
When you take up a hobby, isn't the goal to progress with it, eventually? Of course the main goal is always to have fun, but if you're given a chance to evolve your skills related to it, why not take it up?
Let's take a random hobby - knitting, for example. If someone else, more experienced, who does knitting for a longer time than you do comes and tells you: "I think that's a very nice effort! I really like how you did this and that but maybe you could work on your technique with Z a bit", why wouldn't you see this as a chance to think certain things through and not get angry as if they were purposefully trying to personally offend you?
And I get that there might be some things that people don't like to hear. But you know what? I think that sometimes, in certain cases, people should listen to things they don't like. In fact, I would say it's helpful. (Even more so because at times it feels like a lot of people have trapped themselves in their own personal bubble and refuse to listen to things that could make them even slightly unhappy.)
So, yes, I do think that constructive criticism - when it is actually constructive and not just hate, of course - should be brought back. (I do believe it was somewhat prevalent in the older days of fandom.)