I think it's really impossible to tell what someone else's motives are, even when you have known them for a long time. Who are we to judge what someone else is thinking? As you pointed out, many hackers have a burning desire to know how the thing works, how to break into it, but don't have any intention of doing harm or committing crimes. How else can you learn, but by asking?

Even so, it's important to weigh the amount of harm that could be done with the information, against how well you know or trust the person. It probably wouldn't be a good idea to give someone root password, or instructions on making explosives, unless you felt you could trust them with your life. Similarly, you might tell a relative stranger about exploits that have been patched, but maybe not about the ones you just discovered today.

Not everyone who can pick a lock is a locksmith. But lock-picking is one of the skills that a good locksmith needs to have...