It is completely unfair.
I've had matches with smurfs as well, back when I bothered with ranked, but there are also people who use smurf accounts on normal just to get the thrill of beating people up. Now you're going to hear from Riot white knights about all the wonderful excuses they use to justify it, but in the end, here's my view.
They are cheating the system. Pretending to be a rank you aren't to help level your friends on another account is just as much of a banworthy offense as anybody buying any kind of MMR boost. Anybody who smurfs as a diamond or plat to help their silver or bronze friends level up to a tier they don't belong in should lose their highest ranked account PERMANENTLY, and their other account suspended for a year from ranked play and all their rewards revoked.
With that said, because of the number of people who smurf and the money Riot brings in from those accounts they will never do a damned thing to make the ranked system truly fair. So, you can put up with it or do as I'm doing and leave this game (mainly due to the fact the new client they forced on us is worse than the old one made 7 years ago, if that's possible) because things aren't going to change. Riot's view is its all our fault, its our internet, its our computer, its never them. Ever.