Is the practice of tantric sex dangerous because it seeks to invoke outside energies? Will that create risk of spirit possession or extraterrestrial manipulation psychically?

This, in fact, is a risk. Anything the person does to manipulate their energy can be a rearrangement of the auric field and this can be taken advantage of by spirits who may be hovering, looking for an opportunity to gain a foothold. Particularly when something from outside the self is being summoned, and this is done without divine protection requested in advance, the person is opening themselves up to an incursion and this can be capitalized on by the interlopers, to gain entry readily. So it is not that the desire for an extraordinary sexual experience is wrong, it is simply that in order to have the energies of Gaia enter and serve to supercharge the body to bring it into healthy alignment and give it the fullest expression, the act of the requesting being non-specific in the sense of safety, creates a hazard that is unanticipated. It is much like opening one’s door and calling out to have something come in that is wanted without realizing there may be many sources, many voices, many entities who could take an interest and accept the invitation as being for them when that is not intended. But being blind to the energy oneself, as the physical human almost always is, creates an added vulnerability as the person will never realize what has happened until it is too late. Putting safety around the work is the answer here so the experience can be requested and lived without risk and to have the joy intended without a downside. It is simply a matter of asking the divine realm to keep both parties safe during their time together and to allow the desired energies to be summoned, but to exclude anything that is of the darkness.