I personally think bunk beds are fantastic for siblings. I had them, husband had them. My two boys got them at ages 3 & 5. Now 6 & 8 and all is great.
I have never worried that they would be hurt. We explained to my boys the safety concerns and they take them seriously. Bunk beds are not a jungle gym and are not treated like one. No jumping or horseplay. The oldest sleeps on top and climbs down as needed. Youngest sometimes gets up there to watch a show or read with his brother. Their beds are in their bedroom (sleeping & dressing only), and they have a separate play room for toys and such.
While of course there are bunk bed related deaths every year, I find it rather dramatic to not get them for this reason. Your kids have a much higher chance of dying in a car accident, but I'm guessing you have a car. Anyway, I would say that if you have a child that doesn't understand safety rules or has a hard time following directions and instructions, then bunk beds would be a bad choice.