Any thoughts? What are the causes?

"Since 1998, when a homeless person broke into Mackenzie's mausoleum for the night, Greyfriars Churchyard has been the epicentre of an escalation of unexplained events linked to the ghost of Mackenzie; known colloquially as the Mackenzie Poltergeist. The Mackenzie Poltergeist has been called the most well-docuмented paranormal phenomenon in the world.[6] Even before 1999, there had been reports of unusual disturbances in the graveyard. Between 1990 and 2006 there were 350 reported attacks and 170 reports of people collapsing.[7] Visitors reported being cut, bruised, bitten, scratched and most commonly blacking out. Some complained later of bruises, scratches and gouge-marks on their bodies. Most attacks and feelings of unease occurred in MacKenzie's Black Mausoleum and the Covenantors Prison. In 2000, an exorcist, Colin Grant was summoned to the graveyard to perform an exorcism ceremony; he was said to have picked up "evil forces" and claimed that the forces were too overpowering and feared that they could kill him. A few weeks later, he died suddenly of a heart attack.[citation needed][6] Edinburgh City Council closed off that part of the cemetery until an Edinburgh-based historian and author, Jan Andrew Henderson, persuaded the council to allow controlled visits to that part of the churchyard and in turn this developed into a nocturnal guided tour, which became a local attraction. Greyfriars Churchyard and, in particular, MacKenzie's Poltergeist, have been featured on paranormal TV programmes, including Fox's Scariest Places on Earth, and ITV's Extreme Ghost Stories."

http://en.www.wikipedia.org/wiki/Greyfriars_Kirkyard

It's said that this is the most haunted and dangerous graveyard in the world that the paranormal activity there can kill or lead to death? Aren't the "undead" if they exist just demons masquerading as a deceased person?

Stay away from unconsecrated grounds.

I remember when Cardinal Manning of Los Angeles allowed a well known
abortion doctor to be buried at Holy Cross Cemetery. However, he
forbad a Traditional Catholic from being buried at Mission San Gabriel
Cemetery.
Now any tom, dick, and jerry can now be buried in a Catholic Cemetery.
I know of well known ɧoɱosɛҳųαƖs now buried at a Catholic Cemetery
in Long Beach, CA.

Question is why do secular or non-christian graveyards attract these things such as the "undead/ghosts" who are said to be actually demons masquerading as the deceased for some reason?

What does this do to a Catholic Cemetery that has been used over a 100 years for
a Catholic burial of those that died with the good graces of the church.
A novus ordo bishop allowing notorious and public mortal sinners burial in a
Catholic cemetery.
I heard a program on restoration radio in which this was discussed by Bishop
Sanborn. If a public sinner buried by mistake in a Catholic Cemetery and
became known after the burial, the remains had to be exhumed and expelled
from the cemetery, and the grounds be reconsecrated by a Bishop.