ANY heating device can get hot enough to start fires and/or kill your animal. ANY heating device, whether it's a lightbulb or halogen, or a heat mat or cable. They are all as dangerous as each other, but there are some brands/models that have less quality control and therefore should be avoided. I'm not even going to bother getting into a whistling contest regarding the serious dangers of these devices...they are dangerous because they convert electrical energy into heat energy and the heat they can produce is potentially enormous. It's as simple as that.
ALL heating devices MUST be controlled by thermostats, and a thermostat that turns off the devices it controls in the event of a thermostat failure. A thermostat that doesn't do this is not adequate for the task and therefore should never be used to keep reptiles or any animals for that matter. This isn't a freezer or a fridge or oven we're talking about, this is a heating device used to heat an enclosure housing a LIVE animal and usually situated on a bench or surface that can easily burn or catch fire if a certain temperature is reached.
It's a common sense thing, really, and should always be observed. Yes, I know it costs money for decent thermostats. No, I don't care if anyone thinks it's more economical to just forget about thermostats. It might save you money, but it may cost you your animals, your house, and maybe even your life and your family. You want to take that risk? There's no way in hell I would. No way in hell my animals, my family, my house and my life are worth less than the $100 or so it would cost for a decent quality thermostat.
That is how you must think about this issue. It's a safety issue, that is as far as I'm going to take the discussion, and as far as I'm concerned everyone should be required by law to use a thermostat with these devices - just as they are required by law to use a smoke detector.