What is needed to power a netgear switch with an ATX style PSU?
Let's look at the general case, where you want to apply any kind of power to any kind of device, and the answer, intuitively, is yes, you want to have protection.

Overvoltage protection is installed so that, in the event of a failure, if the AC side decides to come visit the DC side, nobody gets hurt, and hopefully nothing else down the line gets destroyed. Short circuits can leverage a massive flow of current, leading to various faults up to and including fires - so we use fuses, PTC resistors, current limiters and various other tricks to prevent adventurous persons with paperclips from losing their eyebrows.

The good news is that if you are using a ATX power supply that meets or exceeds the actual specifications for a typical ATX power supply, and hasn't particularly been modified, you almost certainly already have most of the protection you would reasonably need to power said switch.

Now, I don't know that I would personally sacrifice all the space an ATX PSU takes up to do this kind of thing for two switches, but I get the feeling you might just be trying to make it work with what you have. In any case, as long as you remember to unplug the thing while you're working on it, this should work just fine, so long as the 12 volt rail can actually support all the load you're adding to it. Without posting numbers, you're the only person who can gauge that.