Section 2 contains: A PATCH request can be issued in such a way as to be idempotent, which also helps prevent bad outcomes [...] Clients using this kind

Section 2 contains: A PATCH request can be issued in such a way as to be idempotent, which also helps prevent bad outcomes [...] Clients using this kind of patch application SHOULD use a conditional request [...] For example, the client can use a strong ETag [RFC2616] in an If-Match header on the PATCH request. So you can, but aren't obliged to.