It's not dangerous in practice. Reading through NEC in the US, there's plenty of leeway for mixing ampacity ratings on circuits, within certain limits. For example, it's fine to have 10x 15A duplex on a 20A circuit. It results in less wiring, and allows for logical grouping of circuits. Electrical code starts from the the most common causes of electrical failures, and tries to design down from there. The ampacity ratings on devices and various components of the circuit are designed to reject the common causes of failure, and conductor failure at the device isn't one of them (appliance manufacturers are more likely to get their devices certified, so if there's a failure in the appliance, some other part of the appliance's electrical system will fail before the conductors do).
So the ampacity of the connector (duplex and plug) is meant to reject certain combinations (plugging a 30amp appliance into a 15amp duplex/circuit). It's obviously very easy to get around that by just wiring things together wrong (18AWG wire on a 30Amp circuit), but by design, a 30amp appliance with the proper plug cannot be plugged into a 15amp outlet.
Of course, this is informed by the electrical code in my home country, so I understand that other places and people have different experiences, but electrical accidents have been on a steady downward trend since the 80's, so the NFPA NEC has to be doing at least some things right.
So the ampacity of the connector (duplex and plug) is meant to reject certain combinations (plugging a 30amp appliance into a 15amp duplex/circuit). It's obviously very easy to get around that by just wiring things together wrong (18AWG wire on a 30Amp circuit), but by design, a 30amp appliance with the proper plug cannot be plugged into a 15amp outlet.
Of course, this is informed by the electrical code in my home country, so I understand that other places and people have different experiences, but electrical accidents have been on a steady downward trend since the 80's, so the NFPA NEC has to be doing at least some things right.