What happens if two of your drives fail simultaneously? This is not as unlikely as it sounds, since those drives were almost certainly manufactured, bought, and installed more or less at the same time, meaning they'll meet their MTBF at the same time. Yes, the M in MTBF means "Mean", but they're still all going to be reaching the end of their expected life at the same time. And when one drive fails, the demand on the others goes up a lot when you rebuild the RAID, increasing the chance of failure even more.
What happens if you get filesystem corruption? Yes, it happens, no matter what hardware or what OS. My university had a massive RAIDed file server whose controller decided to start randomly corrupting things one day. Good thing they had everybody's files on tape, because that RAID was toast, and any RAID would be under those same circumstances.
What happens if your house gets hit by a meteor? Yes, the meteor is fanciful, but building-destroying events are not. Meteor, flood, fire, whatever, RAID helps not a bit, because your redundant drives all get smashed/wet/burned at the same time. And even if you think that these are unlikely, what about a miniature flood caused by somebody spilling their Supersized Coke? Or any number of minor domestic accidents....
If you can't lose the data, you must have offsite backups. If you can lose it, why bother with RAID?