"... due to an unfixable security flaw in the way funds are now transferred electronically, worldwide, it is no longer safe to write personal checks" - Donald Knuth, on reasons for no longer writing his famous reward checks. Google for more info.

The way that ACH transfers is broken and a check contains all of the information you need to generate fake checks and/or initiate ACH transfers.

The bad experiences stem from the fact that handing someone a check is literally handing them your bank account, and asking them to only withdraw as much as you wrote on it. There's essentially no protection except in the form of after-the-fact insurance to get you some of your money back in some situations.

Which is similar to credit cards and debit cards, really. Sure, with CCs you can do a charge-back - but that's just a form of insurance. If the person who got your money withdrew it and left, the CC company would be left paying out of pocket (hence the large interest rates).

It's ass-backwards. Since the internet appeared, banks should have been giving us ways to safeguard against this - for example, fixed-value transactions with a unique key. But we've got essentially nothing.