My build doesn't have enough USB ports. Are USB hubs really that dangerous?

Generally the only ones to be worried about are powered hubs, the only downside to unpowered hubs is they're usually limited to 4 ports and often usb 2.0. That's not an issue if you use it for things like mouse, keyboard, headphones, controller (that's what I use mine for) and use your on-board ports for the things that may draw more power like a mic, mixer, or camera. Unpowered hubs aren't 100% unpowered, they can still provide the small amount of power that's needed for wireless receivers, controllers, or an rgb keyboard/mouse. They can get overloaded if you were to plug in something that requires more power though so if you have connection issues that could be a reason. Also if you plug the hub into the case's USB port that should 100% prevent any possibility of the motherboard getting fried, if anything it'd just kill the USB port. You just have to make sure you secure the hub well if it has a short cord, you don't want it dangling off the case as that'll stress the cable and can cause it to prematurely break. I personally use Anker's 4 port hub, it's $15-20 and works well, the off-brand ones aren't much cheaper and often have more quality control issues than Anker does (though there are other good brands too). I was previously using a Rockband 4 port hub from my PS3 and it still works perfectly over a decade later, though it's case is broken.