To be honest, it's probably the safest bike I've ever owned. I've rode on and off and never had the money or the need for anything flash, so I've always had old heaps of junk and hand-downs (which is exactly what this is courtesy of a broken hanger). It's an MTB and I've had it through plenty a forest around the north east, at speed. It's been thoroughly tested.
It's interesting though, being new to these forums, it's all subjective. You see it as dangerous compared to what you're used to, but I see it as safe compared to what I'm used to. With a little bit of common sense you can judge how much pressure that metal is going to take and you can form your own risk assessment. It may not be 100% accurate and you know there's an element of danger but it's what I've been doing since I was about 7 years old. When I do have the money I'll happily buy myself a new bike, but until then I don't have that priveledge of choice in the matter.