I would like to respectfully disagree with this argument that Dumbledore is evil and/or responsible for the majority of the bad things that happened in the wizarding world. I will begin by trying to refute its premises, then by proposing the premises and conclusions of my own, alternate hypothesis.
Firstly is the idea that Dumbledore being evil resulted in his sister's death. This is perhaps the most difficult premise to dismiss because we know so little about what actually happened between the four teenagers. What we know is that Ariana died, Grindlewald scarpered, and Aberforth blamed Albus for her death. Also that Albus does not know who cast the curse. While I do assign responsibility to Dumbledore for this tragedy, I cannot designate him evil for it. No doubt his judgment of Grindlewald was awful; to allow someone like that close to your family is ludicrous. However, based on what is in canon, it seems that Albus went to his brother's defense when Grindlewald attacked. Clearly this is a familial reaction, and one impossible to an evil character. What would Voldemort have done? He would have killed any and all that stood in his way. Dumbledore defended Ariana and Aberforth, even though their deaths would allow him to conquer the world. If nothing else, he has a conscience.
Secondly, the development of Tom Riddle being blamed on Dumbledore is simplistic at best. From the start he told us that he had reservations about Tom, but he did not suspect that he would become the most evil wizard to ever walk the Earth. Furthermore, the power to allow or disallow a student admission into Hogwarts did not yet reside with him (if it ever did, we don't know how that is handled). He was merely the transfiguration teacher at the time, and he did not become headmaster until after Tom graduated and moved on to Albania. Indeed, Riddle knew that Dumbledore was the first to suspect him of opening the Chamber of Secrets and that it would be nigh on impossible to do it again while still in school.
The claim that education should be denied to those not worthy of it is a ridiculous way to approach education. Who can decide who is worthy and who isn't? Is it not possible for people to change, especially given the empowerment of an education? Denying an entire house of an education just because they believe something different from you is not only illogical, it is flat out immoral. It violates nearly every conception of freedom that humans have ever believed in. And in a more practical application, it has been shown that when a group is treated with discrimination, when they do rise to power, they will act more harshly and bigoted than ever before.
With regard to the Order of the Phoenix and their supposed ineptitude, I cannot help but disagree with you. Indeed, it is much more due to Voldemort's immense talent for spreading fear and enmity than the Order's lack of action that resulted in the first war going badly. He is extremely good at being evil. That can be blamed on no one else but Tom himself. Again, Voldemort caused Sirius' death, not Dumbledore. If he had done this, if he had done that, Sirius might still be alive. What ifs are not reality. The absence of proof is not proof of absence. In effect Dumbledore's inaction had many consequences, but proposing hypothetical alternatives reveals just as many possible consequences, and Voldemort will use every conceivable scenario to try to maim and kill. At the end of the day, it comes back to Voldemort, not Dumbledore.
Finally, the idea that he did not know who he was hiring for DADA is actually incorrect. He knew exactly what he was doing for each hire, with the exception of Barty Crouch Jr. Why would he have set Snape on Quirrell if he did not know Voldemort was possessing him? Of course he knew. The real question is, what did he hope to gain by keeping Voldemort close? He knew Gilderoy was a fraud and Umbridge was power hungry. However, both the curse set by Voldemort, and tactical maneuverings demanded that he act as he did.
I do not believe Dumbledore is a great person. I don't think he is a role model, or a grandfather figure. I think he is human, and tries to stand up for his beliefs in a way that respects those around him. I don't think that is a bad thing. He is definitely flawed. He is arrogant, self-oriented, and secretive. However, he is also trusting, intelligent, and understands his weaknesses. Overall, he has good and bad traits, just like anyone. Remember when he talked about his mistakes being far more significant than the mistakes of most people, even though he made less of them?
In the end, we are judged by our actions, not our intentions. Dumbledore was friends with Grindlewald. But he later defeated him. Dumbledore was using the cloak the night the Potters died. But he gave it back to Harry, rather than keep it. He destroyed the ring, even though he was originally tempted to use it. I think in general, Dumbledore is just easily taken in by the small picture before regaining sight of the big picture enough to salvage the situation (e.g. planning the destruction of Voldemort, but coming to love Harry).I hope you take this in mind. Dumbledore is a complex character and much more difficult to place than being simply evil or good. There are varying shades of gray therein.
Thanks for reading!