As others have pointed out, iCloud is just Apple's version of cloud storage like many other companies offer. If you stay with a major company, you are relatively safe that your data is backed up and secure. Google, Dropbox, etc. are other examples of companies whose very existence would be threatened if they fail to provide reliable and secure services.
There are some givens that apply:
- Hard drives can and do fail
- You will sometimes fail to do regular backups
- Fires, hurricanes, earthquakes, burglaries, etc. do happen
Cloud storage protects you from all the above. And, one of the major advantages of cloud storage is that you are freed from being tied to one device. Using cloud storage allows access to email, documents, photos, etc. from a PC, smart phone, tablet, etc. seamlessly.
And cloud storage is here to stay. Use it or not, but you will be missing a major advance in data management without it.
And, as someone also pointed out, giving your credit card to any clerk or waitress/waiter is a bigger risk then you take with knowledgeable use of the Internet.
If you click on a link to a known company in an email that is faked to look like UPS, FedEx or any company but that is in fact a hacker, your regularly backed up data on your own PC is up for grabs.