A list of things that will prevent us from venturing into space before we destroy ourselves -
1. Religion - When you know how mindbogglingly vast the Universe is and that, we are not the center of anything then how can you expect that any aspect of God trolled your ridiculous little planet. Either God must be an Alien or you are living in a fools world. There is nothing special about this place we call Earth, just home. Ancient wisdom is good only up to a certain point. Beyond that we must place our trust in Science and zeal for innovation/invention. We cannot control our own lives but feel at liberty to talk about the mind of God or Universal reality without any kind of investigation or research.
2. Delay in the arrival of Quantum Computers - Internet revolutionized the information age, but Engineering revolution can only be achieved if we have access to Quantum Computers. Quantum Computers are essential for our survival. Without them we cannot have most optimized solutions for our Engineering problems quick enough. We can have Technologically Super Civilization only if we have Quantum Computers.
3. Science - Physics is not advancing fast enough to build us Artificial Gravity, Faster than Light (FTL) capability, Anti Radiation shields/medicines etc. These things are essential for the future survival of our species in Space. Theoretical understanding of various sciences greatly increases our innovative capabilities and we build greater things. Progress of Science and progress of technology & Civilization run in an eternal feedback loop. One only complements the other.
There is also an unknown danger of Theoretical limitation imposed by Science itself. FTL itself may be theoretically impossible/improbable. Or it may turn out that we may never be able to build FTL due to our inability to conjure/comprehend the energy requirements to bend even immediate space and create gravitational waves. And when that happens, it would be equivalent to going into psychological depression or committing suicide.
4. Our Self destructive tendency and aggression towards each other - The list goes on with Deforestation, Chemical warfare, Global pandemic etc. It will be a miracle if we don't Nuke each other for resources till we start mining Asteroids for those resources. Only faster access to stellar resources will prevent us from killing each other.
5. Premature Alien Contact - Stephen Hawking already warned us that a premature Alien contact will result in the same fate that Mayan, Aztec and other American Civilizations suffered at the hands of fewer but Technologically superior Spanish invaders. At the very least we will just loose our freedom or in the worst case; complete obliteration.
6. Vast Stellar Distances - In our Universe, Galaxies collide with each other all the times without destroying most Stellar objects. This is due to unimaginable stellar distances between Cosmic Objects. Human mind cannot comprehend the vastness of the Universe or even Galaxies unless you start mapping/touring the stellar distances. These distances are so great that they may affect us to go into a psychologically enclosed mindset and that we may never want to leave the comfort of our Planet and immediate Neighborhood.
7. Cosmic events beyond our control - This list goes from known dangers to unknown dangers. Rogue Asteroids & Comets are least of our worries. There are Black holes, Supernovas, Quasars, possible existence of a twin star (destroying life every 27 million years) and other stellar objects being affected by Gravity. Life on Earth is hanging on a vulnerable balance.