(Can people normally make themselves scared by imagining things?)

That's pretty much how severe phobias happen, yeah.

Possibly. When I imagine approaching and playing with it in a controlled setting, I imagine myself being nervous, but not scared. I expect desensitization therapy would work, but only if I actually did it, not merely imagined doing it.

Imagining doing it works for other people. If you can figure out how to imagine like them, it'll work for you too.

(Can people normally make themselves scared by imagining things?) Yep. Some people get more scared than others. Last time I tried I got my heart rate to raise 10bpm, which is significant but much less than terrified.

Yeah, want the addiction. That yields "Aw crap, I had to inject heroin today but I spent all day on Reddit instead. Should set a timer to remind me next time.", which isn't the behavior exhibited by someone currently addicted.

No, that is not what I'm talking about. You don't get paid for injecting, you get paid for credibly convincing people with fMRIs that you crave it. If you have akrasia problems about shooting up heroin it might turn out like you say, but if you think about it in the way that gets your motivational systems going, you'll start to crave it.