I'm reminded of how most all the hallmarks we attribute to the Spartans turns out to be literal hearsay of the time (much of it emanating from...yep, times of conflict/rivalry). Although they were apparently intentionally secretive, it's pretty easy to imagine some not-anthropologist merchants passing along gossip which gets taken in by the rival permanent settlements.
Not that Carthage is free from accusation, but I'm reading some historians actually claim Romans found the religious ceremony of sacrifice to be abhorrent, as opposed to the more general infanticide that was recorded throughout the larger region (including Rome) for presumably a more eugenic/pragmatic purpose.
Sometimes dismissing evidence because of perceived bias is simply incorrect.
I also didn't dismiss potential evidence for Carthage's sacrificial culture, of which there's enough to make the accusation, but really, only that.
I don't actually have a horse in the races of dead people, but I do hesitate to perpetuate even ancient culture wars. It's usually just going to make more use of people's tribal desire than their deductive skills, though why people have emotions about ancient, dead societies, I'll never know.
Now imagine Carthage won the Punic wars and destroyed Rome, what would we be disgusted with while reading about Roman customs? What would we be considering brutal, awful and barbaric?
It's also generally absurd to think that I must automatically be influenced by some propaganda if I consider plausible the ancient records and evidence of another society's extreme sacrificial practices.
As another comment in this reply thread mentions, (though it mistakes Aztecs with Maya), people spent decades thinking that accounts of mass Aztec child sacrifice were colonial era-biased exaggerations, until mass graves of children were much more recently found showing signs not only of sacrifice but torture in advance (to induce tears for the god Tlaloc among other reasons).
Sometimes historical cultures are just awful in certain ways that have to be mentioned in posterity, even if we can appreciate other aspects of those cultures. This applies to any culture and should.
Before you sympathize too much with Carthage, bear in mind that their (well documented by contemporary sources even if you account for anti-Carthagian propaganda from some Roman sources) religious practices were distinctly grotesque, involving no shortage of child sacrifice that even included burning children alive. Notable families were also encouraged to do the same to their first sons in times of crisis, but would often buy the children of poor people to go in their place.
I know the Romans really, really disliked the Carthagians, so it must have tainted their view on them in all circumstances, but even then, there are enough sources professing outright disgust about their sacrificial practices to give the complaints some weight. And if Romans of all people are disgusted with how brutal a country's cultural practices are, you can imagine that they probably were pretty damn awful.