Problem is linking protect with any move, or linking protect with a boosting move. Talonflame is the obvious abuser of this. Linking protect with Brave bird means it can revenge kill a pokemon that usually would be able to take one brave bird, but not two. For example Mega Diancie is now, essentially OHKOd by the smogon bird. Same with Breloom, Azumarill ect.Its also worth noting that if a pokemon linking Protect with a move is facing off against a pokemon with two attacking moves linked, by the end of the 2nd turn they would both have achieved the exact same thing in attacking twice, there is no real clear advantage.
That said though, this is assuming Protect fails each consecutive use, which won't always be the case. But more often than not it should be so you'd be better off with a different link.
I see no problem with Protect shenanigans.
Using protect with Swords dance also increases its attack by 2x, provided you're faster than the opposition. You can do this every other turn, essentially giving you contrary. But this does not only apply to Talonflame, every single (fast) pokemon has contrary provided they want to give up their link.