default_scope bring some degrees of convenience, however, most of the DB queries are application logic. Applying default_scope may payoff when filtering out soft deleted object, but most of cases are rarely justified. Even you could identifid the where clause from SQL log, the situation quickly becomes ugly and turns into a horror movie when joining multiple tables with default_scope. Modifying those queries with unscope is risky and query specs of such are likely to be not fully covered to provide the safety net.
By my colleague Tony.