Just my 2 cents on this but I think the reason the suns UV rays are said to be harmful is completely different from why it is warned against looking directly at a UV flashlight.
By definition, ultra violet is a wave length that is at or just below the spectrum people are able to see. This is why things of certain colored items seem to flash brighter than others under UV lighting.
Basically, a 1000 lumen UV light is exactly as bright as any 1000 lumen flashlight. Our eyes just think it's not but the brightness is still there. So walking around a house with the lights turned off with a 1000 lumen white flashlight is just as straining to your eyes as walking around the house with a 1000 lumen UV light. No more, no less damaging to your eyes.
The sun, in comparison, is a billion lumen mule pumping out all sorts of colors, radiation, and heat.... from 90 million miles away. Since (much like bass sound) low frequency wavelengths like UV tend to travel further than higher frequency wavelengths (namely, the light we can see), the UV light hitting is from 90 million miles away are much more intense than the light we actually see. Hence the suggestion to use UV blocking sunglasses.
I might not be 100% accurate in this tho. Bottom line is, be safe, use protection. Avoid unnecessary child support.