Mystery about Engineers

In first Alien film, Ripley said the beacon from Engineer ship crashed on LV-426 didn't sound like SOS, it sounded more of warning as to keep anyone away. Prometheus showed drawing of Engineers in cave pointing at stars as invitation. Did the Engineers really intended to containment the Earth with black goo and seed but not the xenomorphs they crashed with on LV-426? What’s point of harvesting genetic materials from humans if all eggs hold genetic materials from one person, not society gene pool? It would make sense if each xenomorph can lay eggs like queen, but there is only one queen per colony and if a queen really does collects genetic materials into eggs, it would be from one person, not society. What if that person, host for queen, has dysgenics or some kinds of anomalous genetics apart from most people, as a queen lays thousands of eggs carrying that anomalous genetics? Then the Engineers collect all that? It doesn’t make sense for Engineers needing our primitive genetics when they can do genetic manipulations. Was that ship crashed on LV-426 on way to Earth or elsewhere? Is it strange of Engineers sending warning from crashed ship with xenomorph eggs but sending invitations from a planet with black goo & seeds? I don’t think Engineers are that naïve about what black goo and seeds would lead to.