While I approve of banning cheaters, these guys just aren't cheaters. They're abusers, not cheaters. If something can be abused, something in the game, they'll do it. And quite frankly, this doesn't even hurt the other team, just their own. These guys should be banned as much as team-killers in hardcore mode. These guys are as much cheaters as say the one-man-army infinite grenade glitch in Call of Duty. http://www.youtube.com/watch?v=BfpCn_kuBKs
Its extremely cheap, and definitely not playing how it was intended, but its simply not cheating. I think a temp-ban would have served better, maybe a week or two vacation from the game for them.
If they were to actually alter the game though, actually hack, no problem with a permanent ban. While there are plenty of glitches and exploits that work in this game (such as spawn mortars) or really any game that are cheap, they should never be equitable to actual cheating, no matter how bad it gets.