Yes I must agree that only in Republican France, which had murdered the previous Bourbon, (apparently to make way for another, albeit more enlightened, autocrat) was he seen as legitimate, and let us be clear he was allowed to become First Consul only because the Bonapartes... ahem... removed the Directory. To the other powers of Europe the line of succession had been broken, and a man without link to the royal family had taken their place on the throne.
Look at the Jacobite succession crisis in Britain. James II was a catholic, and so he was ousted by the government and his son in law William of Orange offered the throne, which passed back to the last officially Protestant Stuart monarch, Anne. When she died the Elector of Hanover got the job, much to the outrage of James II's supporters who proceeded to launch 4 large scale rebellions between 1689 and 1745 and numberless plots. To the Jacobites they were merely the supporters of the rightful king with the strongest link, albeit legally disbarred on religious grounds, whereas the new House of Hanover branded them "Pretenders", had they won the throne, the Hanoverians would have branded them usurpers, a name which the Jacobites had already branded George I with.
Something to some is not the same to others. There is no propoganda about it. Legally and some have been playing with legal niceties to defend the death of D'Enghien while apparently condemning Ney's and labedoyere's executions, legally he was defined as a usurper in Europe because he took the throne.