The idea that portals get opened and evil spirits pour through it just because your deceased loved ones come to communicate with you is superstitious thinking. Your deceased loved ones are around you often. They no more bring negative 'stuff' with them when they visit by themselves then they do when they communicate with me. I suppose there are those who believe that evil spirits can 'slip in through the cracks' and into this reality during a reading. Please let me assure you, there are no cracks to slip through.
I realize that there are television shows that depict "ghost hunters" that purposefully go into haunted places to gather evidence of the afterlife. These hunters taunt the spirits in an effort to get them to leave evidence on their technological "ghost hunting" devices. Often times the hunters will report the ghosts following them home and subsequently creating some sort of evil havoc in their daily lives. I will say here that If you go to haunted places looking for cranky, negative spirits, you will probably find them.
And let me point out that if one goes to hunt something that they can't see but that is perfectly capable of seeing them...who's the better hunter, who becomes the hunter and who becomes the prey?