Think of their automatic rebooking as a helpful feature (a rarity with dl.dumb). But in this case your flight booked won't work at all, so they rebook for you but still will give you the option to cancel with a refund, or to try to rebook you on a reasonable alternative flight. Nobody wants to have the schedule changed in this case, but the auto rebook w/flexibility for the customer seems like the best way to handle this type of an issue.

Look at the schedule change as a chance to reconsider flights that may have been more expensive than what you booked. Definitely take a look at your options! For example, I had an evening flight schedule change about 7 mo. in advance that would have caused a misconnect on an overnight flight (but the tickets saved me $150/pp). Delta happily rebooked me onto a flight going in much earlier on day of departure that would have cost me a lot more to purchase, and gives me an extra day of vacation time.