It's a little of column A, a little of column B

Yes, it's true that some dog breeds have been bred to be more aggressive- but aggressive can mean many things.

I was roommates with a guy who had a Pit bull. Awesome dog, great with the kids. Never seen her so much as growl at a person. Animals though she did not fuck around with. And that makes sense, they were bred to fight other animals. So while they are aggressive, they aren't (naturally) aggressive towards humans, though obviously you can train them to be.

I had a different roommate who had a Chihuahua, Chihuahua's were bred for two things, to be fearless rat hunters and to be burglar alarms. They also have a personality quirk where they typically only bond with very few people, and even then it can take a little while for them to gain your trust. For about the first month after he brought her home she would bark at me every time I entered the room she was in. After she got used to me, she was the sweetest little pup you could imagine. If anyone else came by she just couldn't handle it. If I picked her up and held her while talking the other person she would eventually calm down some, but she still didn't like it. You usually just had to put her in a different room. She didn't nip at them or anything, but if they had tried to pick her up it probably would have been a different story.

Not all Chihuahua's behave like that, but it's typical.

I've lived with a Doberman who was a total coward (and neurotic the poor thing), and a Rottweiler who was perfectly fine with me, until her owner was out of sight, and then she acted like she had no idea who I was. As a kid we had a German Sheppard who was a total sweetie (the kitten thing was an accident), and I used to own a Chow/Lab mix who literally loved everyone and everything.

The breed plays a big role in their behavior, but so does training/ socialization. People who blame it solely on one thing or the other are just wrong imo. Some dogs will never be perfectly chill, but you can train them not to be assholes.