Dumbledore might have started out in the Harry Potter series as an enigmatic but endearing mentor figure who seemed benevolent, but by the end, many fans realized he was much more complex, and even morally grey, than they would have suspected.
Seeing as the Harry Potter series was written in the 90s and early 2000s, there are many things about the series and about the character of Dumbledore that would likely not have gone over very well if the books came out today instead.
Letting Gryffindor Win the house cup
While this might not be a particularly dangerous or evil thing to do, it’s not a very great way to run a school. As Headmaster, it should have been Dumbledore’s job to try to treat each Hogwarts house and each student as fairly as possible.
So, when he awarded the Gryffindor house points so they could beat Slytherin at the end of Harry’s first year, it was a pretty blatant moment of favoritism.
The way he let Snape be his right-hand man
The relationship between Dumbledore and Snape is a rather complicated one. While Dumbledore didn’t particularly like the reasons why Snape betrayed Voldemort, he did grow to trust him completely.
The fact that Snape was still such a bully, manipulative, and even cruel makes it troubling that Dumbledore was willing to trust and use him so much.
Letting Hogwarts be such a dangerous place
Hogwarts seems like a school that always has some element of danger involved, but during Dumbledore’s time as Headmaster, it was particularly bad. Because Harry was at the school, Voldemort was often targeted. However, there were many things in Dumbledore’s control that he chose to allow that put the student at risk.
First of all, he should never have allowed the Sorcerer's Stone to be hidden at Hogwarts. Secondly, he clearly knew a lot of the things that went on, and yet he allowed Harry and other students to put themselves in danger anyway.
That his sexuality was only revealed outside of the books
This point has more to do with the way that Dumbledore was written than the character itself, but it’s worth pointing out as it wouldn't fly so much in today’s cultural context.
Revealing that Dumbledore was gay outside of canon made many fans angry, and this shouldn't’ have been treated as some hidden thing. Also, the storyline with Grindelwald and how the only gay character in the series was handled was pretty problematic.
Letting Hogwarts professors treat their students horribly
Just like Dumbledore let a lot of dangerous things go on like keeping the school open after the Chamber of Secrets was reopened, he also let a lot of borderline abuse happen.
There were no standards of how professors at the school had to treat their students. Dumbledore could have at least stepped in and stopped Snape from bullying Neville to the point that he was terrified of Snape.
Keeping so many secrets from Harry
The relationship between Harry and Dumbledore is also deeply troubling. Harry trusted Dumbledore to tell him the truth or at least tell him most of it. So, the fact that Dumbledore told so many half-truths and kept so much from him was unfortunate.
He betrayed Harry’s trust and kept him in the dark too much. He could have at least told him more about his past, and the fact he didn’t make him seem suspect.
Making Harry live with the Dursleys
There are a lot of things about the decisions Dumbledore made on Harry’s behalf that, at best, don’t make a lot of sense and, at worst, are cruel. While Dumbledore’s reasoning for leaving him with the Dursleys was to protect him with the deep magic his mother left with him, he let Harry be abused for years.
He could have at least explained this before or provided emotional support to Harry after what he went through at the hands of the Dursleys. And, it wasn’t really fair to make Harry live without knowledge of the wizarding world.
Leading Harry As A Lamb To Slaughter
Of all the problematic things that Dumbledore did in regards to Harry, the worst of all was that he suspected and then knew, for a long time that Harry Would likely have to die for Voldemort to be defeated.
He kept this from Harry, and while yes Harry was young, the fact that he was able to lie about this and allow it to happen is messed up.
Being Partially Responsible For Ariana’s Death
In Harry Potter and the Deathly Hallows, it’s revealed that Dumbledore's deepest regret and the worst thing he did was to be partially responsible for his younger sister’s death.
During a fight with Grindelwald, a spell hit Ariana and killed her. While it might have been Grindelwald’s spell, although it’s unclear, he still holds some responsibility for what happened.
That He Supported Bigotry That’s An Allegory For Nazis
Of all the things that would not go over very well about Dumbeldore today, the worst and most obvious is his connection to Grindelwald. Even more so than Voldemort, there is a direct allegorical tie into Grindelwald and a real-life dictator.
There are many parallels between this dark wizard and Nazi Germany. So, the fact that Dumbledore went along with this anti-Muggle rhetoric is particularly disturbing.