Those scenarios are not remotely comparable to the present-day. First of all, in those scenarios the native European elites were still Christians who strongly identified with their religion. They cannot be compared to modern-day elites, or for that matter modern-day European commoners.

Second, in none of those scenarios was the demographic situation comparable to the modern-day situation. You are conflating religious conversion with ethnic replacement, which are not the same thing. Islamic Spain, for example, was never majority North African or Arab, not even in the major Muslim centers like Cordoba and Granada. Even the elites of Islamic Spain were mostly identical to other Europeans in terms of race or ethnicity, let alone the common Spanish converts. Here is a depiction of Muslim elites in Spain, from the Alhambra palace in Granada. Besides their dress, which is North African, they look just as "white" as Spanish Christians. If a Spanish Muslim converted to Christianity, within a few generations of cultural assimilation he would be totally indistinguishable from Spanish Christians, since they were ethnically and linguistically the same (for the most part). On the other hand, a population that is racially-distinct from the majority population will retain its own strong identity even centuries after converting to the dominant religion, as we see in America with blacks (converting blacks to Christianity hasn't diminished racial identities and animosities, even after 300-400 years).