Because there is a good reason for UVB rays. They don't go as deep into the tissues, and thus produce less depth of damage, and do not damage the collagen levels as much as UBA.
In a tanning bed you are getting most all UVA rays. In the outdoor sun you are getting some 5% UVB rays, and the vitamin D that is produced is protecting your health in many ways. Actually, boosting your health.
Emits more harmful rsys
Because it is healthier for your body
A lot of negatives and too pricey! Rather get my Vitamin D and melanin!
You have more control over sun tanning and as you know your own skin (I hope you do anyway) If you use a bit of common sense you'll use the right SPF sunscreen and know when to get back to the shade (sitting under an umbrella at the beach is more pleasant than lying in a tanning bed.
Cancer
No benefits health wise while your body protects you somewhat from the sun naturally. even though this was a con in your article it could be a plus also. The sun is not always there so you will be forced to regulate exposure.
