Psychology is one of my main interests in life. Most likely, people who use aimbots and the like are motivated by either of the following (in no particular order)
1. To express aggression to others. It ruins others games and this may give pleasure (think bullies being sadistic in watching their victim tormented).
2. Power. Over others. Can do what the others cannot. Can ruin their game if they want. Kill them through a wall. A bit like a virtual person with supernatural powers. "You use cheap tactics on me? MKb42 harlot?! I'll teach you a lesson, you skank".
3. Prestige (social status) that comes with being seen as a person with such supreme skills. Narcissistic type - even though it is totally phoney and not something they earned, they may believe that they are awesome enough to have properly earned the glory that such super skills would imply. Most people aren't able to do this, since they can't cheat themselves that easily. Many gamers, especially competitive ones, are deeply impressed by, admire and envy highly skilled gamers. Hell, I remember the buzz around the number one player in Company of Heroes. That guy had (genuinely) genius abilities regarding Real Time Strategy games. And people treated him like some kind of movie star.
4. Cynical, paranoid types may assume that everyone else already does the same thing, (or would if they knew how). They see such things as acceptable behaviour as "everyone can do it". You may have come across people expressing the opinion that using exploits in the maps and bugs of the game is perfectly fine because anyone can use it equally. Same line of thinking.
EDIT: I think I played against a Friedrich using an MG34 on Train Station this morning. He tried to deploy over and over in the same upper floor spot, and I would kill him almost every time with my own already deployed DP-28. But Friedrich is not an uncommon (Germanic) name. Might have been a different Friedrich.