Glitch in the System?

Ok this is really starting to get on my nerves. Every time I play on certain maps I see someone with a sniper get out of the map into areas that are physically impossible to get to, an example would be the map where you are on one of Palavins moons, I see people get on top of the huge rock so they can not be killed or be touched by the enemy. It is pissing me off to see this many people with no guts what so ever to take an enemy head on. I understand that some enemies like the Banshee, Atlas, Brutes and Geth Primes can be a very challenging opponent, especially on Gold and Platinum but that does give these people the excuse to mess with the server to save their own butts. All I have to say to people who do this is TAKE A GOD DAMN CHANCE! Its good for you. Also while im going on about messed up servers, Why do some enemies (especially on Gold and Platinum when it is the most annoying) appear but are stuck in the middle of the air and take no damage? or get stuck in a wall and it takes 10 minutes for them to just die, but by then everyone quit the game so it is not as easy to continue especially if you are on the last wave or something.

The picture below is what I wish many more people were like toward people who do this kind of crap over Xbox Live.