Maybe the DELETE command should be banned from SQL. It was probably invented when the disks were tiny and it might not be suitable for our times, especially nowadays when we talk about things like BIG DATA.
But, one can argue that not deleting can be dangerous, too! One can claim that by refusing to delete we might end up with a lot of old, duplicated, bad quality, uncleaned, irrelevant and untrustworthy data.
Maybe the worse thing that can happen to data is to refuse to delete it enough. Perhaps because of this lack of enough deletes and fear of deletes we end up with all the 'bad data' found in some database systems today.
Whatever you choose to do, delete or not delete, one thing's for sure and that is that you should know what you are deleting or not deleting. Choosing confidently what to delete comes from understanding and knowing your data model, and the implications a delete will have on the data model and never because the data is not required for your project!