I don't think PL'n is cheating at all. Its a choice you make and you character will reflect that choice.
If you want to play the missions solos, you need to go through the game or you lose your contacts. If you don't care about the role play and want to kill and team play, then PL'n is fine.
I spent time doing the missions to get to level 14 with my controller only to not like her and want to use a defender again. I don't want to deal with those stupid missions in the same locations again, it's dumb and the levels suk. My defender is built for team support, so PL'n her to the level of the team so I can actually play and be of use is critical to my gaming experience and needs of my character.
So you don't like someone PL'n to level 20, how do you know that person isn't planning on supporting every hereo they come across? I know if I was a level 20 defender, I would revive or heal anyone who needs it I run across, you telling me those people healing you take away from your gaming experience? they might save your butt when you need it most, and they got to that point by PL'n.
If someone is PL'n just to be some level 50 masta, then yea, thats dumb, but if you are like me and doing it so I can rejoin my supergroup with a defender of great use, I wouldn't [censored] about it.