So, Were They Really So Bad?
Yes. Yes they were. Did we mention the cannibalism? After they removed your heart and threw you down the stairs, they'd eat your arms and thighs, and whatever other bits looked tasty (the nuts? We do not know).
Some historians think that nourishment was the main reason behind all of this willy-nilly human sacrifice, as the Aztecs had no domesticated animals to slaughter, and as such their diet was low in fat and animal-stuff. You know how it is if you've ever had a roommate try a vegetarian diet. It's just a matter of time until you start waking up with teeth marks on your extremities.
And that's not even the bad part. The Aztecs held themselves to a high standard and for every situation they asked, "Could we make this more gut-wrenchingly gruesome?" So, for instance, during the sacrifice to the fire god, a newly-wed couple would be tossed into, you guessed it, a fire. Then, right before they finally died (from their horrendous burns), they'd drag them out, flesh still smoking, and dig out their hearts.
Wait, it gets better! There was the offering to the earth goddess, which involved a young woman's skin being removed and worn around like a Silence of the Lambs-style serial killer flesh suit.
On one hand you might ask why none of the Aztecs thought this was odd. On the other hand, if somebody had an objection to the ceremonies we're guessing they kept that shit to themselves.