I think it's always a good practice to exercise caution and respect for mechanical and electrical devices, no matter how low the perceived risk may be. While standards exist for e.g. voltage or current under which the relative risk is reduced, careless operation of even low-energy systems may at best damage the equipment, or at worst result in injury. It also tends to lead to the normalization of dangerous practices, which transfer to dangerous situations.
PC fans are surprisingly dangerous.
So much so, that Dell and HP are forced to put a little triangle "warning!! fan!" sticker next to the fan in a laptop.
Okay, maybe not. In the case of the blower fans, you are more of a danger to the fan than it is to you. Touching the thin blades while operating is often enough to snap some or all of them off the hub.
On normal axial fans, DIY PC market fans are often underpowered, at 0.1-0.2A at 12 volts. This isn't a lot of power, and the rotation speed is low and as you have found, not very dangerous.
However, outside of the DIY PC market, even in any PSU, fans are often rated at 0.3 A, and the average graphics card fan is rated 0.6 A. Once you get into the several watts territory, the fan is capable of operating at 3000+ RPM. On OEM PCs, 80-90mm CPU fans are rated at like 0.9-2.5A. In servers, fans up to 4A are common. These operate at 10,000 RPM or more.
The reason you do not hear about this is because most systems oversize the fan and run it at a low speed to reduce noise, but keep that machine that is choking in dust running at full speed so the factory floor doesn't halt or something. I have seen Dells in these kinds of situations where nobody will clean the PC in 20 years, but it has to, and does, keep trucking. These kinds of fans produce robot vacuum cleaner territory of static pressure, up to many inches of water column at 250 CFM.
These kinds of fans are extremely dangerous. China/AliExpress calls them "high speed violence fans" for a reason. The motor hubs are usually made of steel in higher powered ones, and the stall torque is high. The blades have a swept, sharpened tip made of glass fiber reinforced plastic, and the blade assembly carries several hundred grams to kilograms of inertial force. These fans will mangle fingers. When I was very young and inexperienced, [warning graphic], I caught my finger on the sharp tip of a 90mm fan from a Dell while it was spinning down. In a separate incident, I also managed to touch a Intel stock cooler on full speed, and the blade got caught under my fingernail.
Always use a suitable fan guard or safety equipment when testing cooling fans or working around them. The more powerful fans will take off chunks of your fingers, and even a tame seeming fan can quickly speed up to dangerous power levels without notice when the system controller senses a case open, fan failure, or high ambient situation.