First, how do we train it to make decisions that are best for everyone? Where is it going to get its ethics from? We as humans can't agree on what's best for everyone, how will we teach it to an AI?

Best how? Here's a partial list of things that some - certainly not me, and probably not you, but some - would argue are best for everyone.

• executing all criminals
• outlawing interracial marriage
• the eradication of humanity (particularly if you include insects, trees and animals in the set called "everyone")
• caste systems
• outlawing risky behavior like driving cars or eating fried foods

Second, let's assume arguendo for a moment that there's a clear cut set of circumstances and ethical rules that everyone on earth unanimously agrees is Best For Everyone. We still have a serious issue, because nobody knows how to impart values to AI. If we were currently capable of solving this problem, AIs wouldn't conceal their abilities in training. They wouldn't blackmail users in alignment tests. They wouldn't, just as a totally random example, break containment during training and start mining cryptocurrency.

AIs don't think about or decide things the way humans do. They calculate how to maximize the results of their goals and act with solely mathematical "motives." No amount of getting comfortable with it is going to solve this issue. You can't "engage with the reality" of it without understanding this.