Are alien portals that are used by the alien spirits to come and go and which enable easy infiltration by spirit meddlers, created by alien spirits or extraterrestrials in the physical, knowing it makes humans vulnerable to spirit possession?

They are indeed created for another purpose. It is a fortuitous arrangement that is known to the extraterrestrials, and this is why it is applied universally throughout humanity. It was initially created as a way to facilitate energetic manipulation of humans and can continue to serve in that respect as well. So you are already dealing with healing of the consequences of any such energetic attacks. Now you are shutting the door to them by requesting removal of alien portals, and a major additional blessing will be their absence from people making it a harder task for spirits to gain entry. This will go a long way towards lengthening the intervals of time when people are free of this menace, and that will facilitate ongoing healing to be all the more effective.