I think Jammerdan’s concern is valid here. You create a bucket, the default grant is to apply everyone access to all your buckets. This is easy to just hit OK and miss that instead of giving Everyone access to that one bucket, you just opened up everything by mistake.
I agree, that people should pay attention. But it would make more sense, in my opinion, that if you create a bucket, that the grant menu defaults to showing just that new bucket as selected. And not All Buckets. It would reduce the potential for error.