Soft Delete VS hard Delete

Whilst I agree soft deletes are nice because it's easy to correct "mistakes" I think there are other implications.

If you have a table that is used in dozens and dozens of queries, then every single query is going to have to include an extra condition on the field that indicates whether the row is deleted or not. Any ommissions here could have undesired consequences that might not be noticed for quite a while. For example the calculation of a customer's balance that doesn't account for invoices that have been deleted won't be noticed until some invoices actually get deleted.