Dick Grayson would be actually the most dangerous villain in the entire DC Comics.
This is because he was molded to be the perfect weapon.
Dick has trained with Batman, Lady Shiva, Deathstroke The Terminator, Court of Owls, Justice League, and Titans.
He has been fighting crime since he was eight fucking years old in fucking Gotham City aka the city with the highest crime rate in the world.
So up to that Dick is one of the most experienced and dangerous heroes in the world.
But these are not the only reasons.
At the circus Dick has learned to mask his emotions and with the passage of years he is one of the most dangerous liars and manipulators (although DC will never admit it).
If Dick suddenly decided to become evil, no one would suspect him (see for example DC Vs Vampires).
Dick Grayson is the heart and soul of the hero community and he is related to basically all heroes and even some villains. So no one could suspect the first Robin, the first sidekick, the fucking golden boy.
And that would turn out to be their death.
Also, Dick may not be the smartest person in the world, that's for sure, but he has been training under Batman for almost a decade and it is obvious that he possesses expert investigative skills, an intelligence out of the ordinary and that he knows the weaknesses of any hero and villain in the world. Dick can defeat others because of his strategizing skills and at the same time avoid being defeated by the world's greatest strategists (such as Batman, Red Robin, Ra's and Deathstroke) because of his unpredictability.
So to sum up, if Dick were to become a villain he would be the most dangerous because: he is one of the greatest fighters in DC, he has trained under the greatest heroes and under the greatest lethal assassins, he knows how everyone else fights and he would destroy them, he would be one of the greatest liars and manipulators if only he wanted to (he could literally bring anyone to his side), he is a great detective and strategist and at the same time unpredictable and impulsive, he knows anyone's weaknesses and he wouldn't hesitate to use them to his advantage, he has been a crime fighter since the age of eight and because of that he is very experienced, almost no one would be able to seriously fight him (because he is a brother, a son, a friend, a student, a mentor, a leader, a nephew, and many other things to most heroes but also villains).
No one would be able to defeat Dick Grayson if only he turned to the dark side.
So yes: think of a Dick Grayson turning evil...
They would all be screwed.
They are fortunate that Dick uses his abilities for good, otherwise they would have to face the most dangerous threat ever, and it is not even certain that they would come out on top against a dark Dick Grayson with no scruples and no morals, with no remorse in hurting his friends and family.
It would take little for Dick to bring down the Bat Family, the community of heroes and even the community of villains.
Dick Grayson would be the most dangerous villain DC could ever have.
And do you know why?
Because he was molded to be the perfect and supreme weapon, capable of taking on anyone and coming out on top, and in the end he could kill anyone without any hesitation.
Dick Grayson is not the universal constant of goodness.
Dick Grayson is the universal constant of competence.