It would be wrong to say that Too Many people are getting the Rinnegan. After The SO6P, Only one other person has had the Rinnegan...That is Madara.
What about Nagato, you say? Remember Tobi-Madara said He Gave Nagato the Rinnegan. I believe he was telling the truth. Tobi Gave Nagato MADARA'S original eyes, in order to use Nagato. Madara planned this before he died. How about Edo Madara? Well that is still Madara's Rinnegan.
What's actually going on is that Madara's Eyes are being shared and Edo Tensei'd. In truth The Rinnegan is still Rare and has only had Two Legitimate owners, that is of course if you give Madara a pass for stealing Hashirama's DNA in order to force the development of his Rinnegan in the first place.
Let me also say that Madara's Rinnegan is not on a par with the SO6P's. Why, well that is because the physical energy that energizes it (Hashirama's energy), is probably inferior to The SO6P's physical energy or even the Younger brother's. In addition, the Spiritual Energy that initiated it, Madara's, is probably inferior to SO6P's, Older Brother's, and maybe even inferior to Sasuke's spiritual energy. In effect, Madara was able to awaken the Rinnegan by using contrived methods. He succeeded, but Madara is probably a weaker Rikudou than the original.