The United States kills off more than a million of its own children every year, while at the same time we allow a million foreign invaders to cross our borders every year.
I don't know if there's anything "Roman" or "declining" about that, but it sure as hell is symptomatic of a deranged social order. I suspect the modern age has brought about a social/political climate where the process of a collapsing empire will occur at a far more rapid pace today than it did 1500 years ago.
Infanticide was rampant and routine for the entire rise and peak of Rome.