Or do they reproduce asexually? Would that mean alien sex doesn't exist? What if they still have libido though?
any sentient sexually dimorphic species will remain in a state of permanent scarcity, war, poverty, crime, disease etc. for however many millennia it fails to control the wombs.
This happens because the male, in it's drive to breed, will do stupid things like crime, theft, war, exploitation, insane accumulation and dissipation of wealth etc. all of which will hamper the development of this society into a sophisticated one, as 99% of male energy (and, consequently, of society's resource) will be wasted by trying to court females.
A verifiable scientific prediction of Marxist-Rodgerist theory is that the seizure of the means of reproduction, that is: putting all foids in a comatose state and locking them in breeding facilities will result in a massive increase of available resources, since males will no longer waste energy trying to attract and/or keep foids.
The Marxist-Rodgerist answer to the Fermi Paradox is that nearly all sufficiently advanced spacefaring societies will be foidless societies, where all females are kept locked inside breeding bunkers and just like they refuse to interact with females of their own species, they also refuse to interact with females of other species. Therefore, the vast majority of advanced alien species will NEVER be in contact with females, and since the female humans roam the surface of the Earth, they will not interact.
And an advanced Marxist-Rodgerist society comprised of spacefaring I.N.C.E.L. cosmonauts will NOT send any "hello" messages to planets with females roaming free.