My nephews who are very active and can be very naughty boys have bunk beds at their dad's place and they (so far) have been Ok. I think it's important to evaluate your own child's ability to be in a bunk bed. It's like pools,kids do drown in pools, but not all children drown in all pools. Bunk beds are the number one cause of bone breaks in kids under (I think it's 12?) but not every child who sleeps in a bunk bed is going to break something.
I think if your child can be educated as to how to be safe in a top bunk, if you have a railing (if neccessary) then it's fine. Just like educating kids how to be safe around the pool. Obviously not something you can teach smaller children, so you need to evaluate your own kids, will they behave and respect what you teach them? They also make bunk beds lower to the ground now, and sometimes have them in an L shape or similar so these may be options for you. Or a trundle bed might be the answer for a while until the kids are older. We don't have big rooms so we are looking at one of those beds that has a desk underneath for our older daughter so I know how you feel.