teachers mostly, sometimes people are curious or think they'll gain power.
2. typically they think nothing will go wrong. so they'll bow before you and do whatever you want. if the person is experienced, they know there's some risk if done wrong, but they know what they're doing, so they probably think the creature will show up look at them, then who knows, ask what they want maybe? i've never summoned anything, but i've gone to the astral plain and dealt with dragons, typically they just watch you until you do something stupid.
3. as said before, not all creatures, such as demons, are evil. not sure what this question is, but i think the answer would be the same, people think they can handle it and very few can. astral beings like demons, spirits, faeries, dragons and whatnot can sense more than we can, so they can tell what someone wants, or how mature they are, or if they summoner is scared. i know when dealing with dragons, you cannot be afraid, or think you're better than them or they'll attack you. personally, i don't see why you would want to summon anything. also, demon's are rare, and you know when they're around. when anything is summoned, though you probably can't see them, things change depending on what yous summoned, temperature, smell, light, you'll even feel different.