The idealistic answer would be that users would only flag real spam and plagiarism but we all know that won't happen.
The ideal would be that this alternative mana bar for flagging is only a fraction of the size of your real real mana bar so it would run out faster so if you want to do positive flagging or bad flagging, you only have so much flags a day, let's say, 3 full flags a day or something like that, therealwolf released another post regarding this and he explains it a bit better.