Perhaps, then, the opposition had more to do with the fact that the hereditary prince's mother was a noblewoman, so in his near ancestry the house of Thurn and Taxis had not intermarried with a sovereign house.

As I understand it, ancestry was irrelevant for a prospective spouse who came from a solidly sovereign house (e.g. Prince Ferdinand of Saxe-Coburg and Gotha). Thus it was that when that german ducal house *slipped* by accepting Princess Mária Antónia von Koháry as a bride, the rest of royal Europe likewise recognized the union as dynastic. As such, their issue were treated as dynasts in a reigning house, as opposed to morganauts.

And look whom the couple's surviving children married: the eldest son became the king consort of Portugal, and the next two married children of King Louis-Philippe of the French.

But the situation was different when a morganaut or member of a mediatized house attempted to marry into a reigning house: ancestry DID matter (the principle of "noble quartering"). There was no way in the world that the Teck and Battenberg princesses (May, Ena, Alice, and Louise) could have been accepted as dynastic brides of members of sovereign houses, had they not been of royal ancestry (three quarters in each case). As it was, three of them alone even became queens!

Because Thurn and Taxis was not a reigning or royal house, Prince Maximilian had to have this kind of ancestry, to be worthy of marrying a Wittelsbach. As it was, he didn't quite have what those afore-mentioned morganaut princesses had ...