i think it depends on what you mean by a bad/negative spirit...i do believe they exist,and do believe i encountered one in my haunting at home..but what i now know is that this/any negative spirit is usually causing a nuisance and the scare tactic for a reason..not cos they want to,or they think oh heres a good opportunity to scare the poop out of so and so..but to use this to their advantage..a spiritual survival technique if this makes sense..with past knowledge its been used in a way to gain the attention they have needed to be aknowledged to be helped over to the spirit world where they belong.
many spirits miss the opportunity to cross over,or are grounded for other reasons,some dont/wont even accept they are dead..so linger in limbo if you like..they simply need a little guidance thats all..even the nasty ones//lol