They didn't celebrate the means, they celebrated the result. The Gauls had brutally sacked Rome in 390BC, and then further humiliated them as they were paying a massive ransom to end the siege. This became a part of the Roman identity and led to an obsession with ending the Gallic threat. Centuries later, Caesar would unambiguously achieve exactly that. In modern times it's hard to understand this because what happened last year is already ancient news, but in ancient times it was not uncommon for feuds, even on just a family level, to last for centuries.

Post-industrialization (kind of assuming they'd have access to modern tech here), slavery makes very little sense - even completely ignoring the ethical issues. Pay a negligible hourly/monthly cost to hire a skilled worker that can be easily replaced or dismissed as desired, or pay a huge up-front cost to take on somebody who is probably low skill, may or may not work out, and then be 100% responsible for all of their needs and other costs going forward? They'd likely outlaw it just like every other country that's gone through industrialization has.

Similarly exposure (which began to be phased out and moving towards adoption once Christianity took hold in Rome) was once again largely a product of technology. Abortion was extremely dangerous in those times for the mother, and exposure was one way it was done relatively more safely. And children were often exposed because of various deformities or their sex which, again, can now be detected at a prenatal stage. Though the sex issue again gets back to a lack of technology. Son's worked and essentially were your pension, whereas daughters joined the house of whoever they married, to say nothing of dowry related issues.

Obviously we have to do a lot of speculation to imagine what a Roman Empire in modern times would look like, but I don't think many of the knee-jerk reactions to it are really justified.