I've switched a 100mW laser diode via arduino before... was making a laser harp...
And, you're somewhat right to be concerned; you likely won't blow anything up, but depending on your driver design, you might have a non-zero turn on time.
The drivers for bigger diodes include feedback and thermal compensation circuitry to prevent you from frying the diode; this will generally keep you from doing bad things to it, but all that circuitry takes power to turn on and off, resulting in a non-zero turn on time. And it completely prevents you from adding a smoothing cap to the driver power supply, cause that'll change the turn on time from msecs to secs
Some drivers are designed to take a TTL input to switch the diode; in those drivers, all the circuitry is left hot when the laser is off so you get very fast on times.
If you can't find a suitable driver (I bought mine off ebay for $20), Sam's Laser FAQ (Google is your friend) has many reverse engineered driver designs.
And finally, what others have posted is right; your 100mW laser will likely only engrave or burn. And that's if you focus it really well, on dark colored material. An adjustable focus rig and patience would be required to cut any appreciable thickness of material. My advise is to pick up a 1W or higher IR diode on ebay... you can get those for ~$20 without any of the extra stuff you need. You'll need a lot of extra stuff though, like:
C mount diode housing (preferably with heatsink)
IR-compatible collimating lens (plastic, not glass, people! glass blocks most IR light)
diode driver (your 100 mW driver won't even cascade the IR diode; it'll light dimly as an IR LED, but it won't lase with that driver)
IR laser safety goggles!!! The good news is that your eye isn't very good at focussing the IR wavelengths you'll use. The bad news is that 1W is enough to do plenty of damage anyways, so play it safe.
IR viewing card (rat shack has these for ~$5)
And if you want the ultimate in safety, a glass aquarium to block the IR light (test with the viewing card + safety goggles) - use it as a cutting hood to block any IR reflections.
I can't stress it enough, even looking at the pinpoint of a 100mW laser focussed strongly enough can be blindingly bright, protect yourself!!!