When they tried to apprehend Klaue they ended up unleashing the Hulk on Johannesburg, Ultron happened because Tony thought he knew best and so Sokovia happened, and when they tried to apprehend Crossbones they got dozens of civilians killed as the least worst outcome
Hmm.. im not certain we can really blame them for getting the Hulk unleashed there. Parly because i cant see what oversight could have done in that situation, besides getting more normal humans killed. The Avengers were the ones best suited for the task. And they still failed.

Ultron meanwhile happend because they muddled around with alien technology. But i still think the reason for doing so were worth the risk. The invasion of New York showed humanity that they were just a small fish, and there were sharks out in the deeper sea. There was a need for better protection.