This is a more fascinating question than many might think at first glance.
Kronos is the Greek god and probably comes from Proto-Indo-European * gern- which meant germ or seed and yields the modern English words germ, grain, corn and kernel. This is likely because Kronos 'begat' the Olympian generation, and therefore was the 'seed'.
Saying the Greeks viewed Kronos as evil is something of a simplification, and it's important to recognize it as such because the difference in Greek and Roman religious worldviews goes to the heart of your question. For the Greeks, the gods showed supernatural virtue and supernatural vice. As can be deduced from his name, Kronos was originally an agricultural deity and the connection of seeds to planting and harvesting crops led to an association with seasons. Kronos wasn't necessarily evil, it rather might be more diplomatic to say that because he feared one of his children would overthrow him (a well-founded fear, it turns out) he was doing 'what he had to do' by eating them.
Saturn's etymology is a bit trickier, but is probably PIE * sewH(r)- which would have meant 'seed, bring forth' and is cognate with modern English seed, son, semen, serum, sow (meaning what you do with seeds in a field). This means Saturn for the oldest of the Romans had an agricultural character (like Kronos for the Greeks) and it is apparent the two entities come from a single concept in an earlier PIE society.
The big difference is for the Romans the gods were paragons of virtue or vice. They were individuals much more to be beheld from afar with a sense of fear or awe; the Greek gods were extraordinarily relatable by comparison. The Roman association of agrarian wealth with Saturn was therefore the chief issue for people, while the conflict between himself and Jupiter was a matter amongst the gods. The Greeks didn't view the behavior of Kronos and Zeus quite so distantly but rather as a plausible human circumstance, and therefore may have been more reluctant to worship not only someone who ate his children, but who lost the war that came after. All fathers worry that their sons will outgrow and eventually overpower them, and the Titanomachy is a mythical reflection of this universal human process.