I find the real usefulness of the label "doctor" is in giving patients the comfort that you know what you're doing, and in different settings that means different degrees. During school I never introduced myself as such, but after explaining "student doctor" to a few patients failed to help them differentiate, I never really corrected them when called me "doctor". We've all worked hard to get our degrees (MD, DDS, DVM, DO, OD, etc.), and we all deserve to be proud. As for PhDs, I happen to know a lot of them, and I can't think of a single one who would want to mislead someone into thinking they have skills they don't, but in the appropriate setting they too deserve respect for the amount of work put in.