There is gravity in the middle of empty space with no detectable baryonic matter for hundreds of millions of light-years in all directions. You explain that without an unseen new matter. That's right. There are massive voids in space, where we can see the galaxies in the background behind them perfectly clear, but we can detect gravitational lensing within the void. Even if the lensing was caused by dust, the sheer amount of lensing would mean an amount of dust that would be easily detectable. You could also say it's a bunch of blackholes that got ejected from their host galaxy and just so happened to not drag any dust along with them. Even if you could accept that, the lensing is so spread out, it couldn't be point sources.
And there is no evidence that smoking is bad for you. Our models are wrong.