True. You can't deny that they often let Valverde follow his own chances instead of sacrificing him for Quintana (even though occasionally it has also been the other way around). It just seems that some people can't get over it and use this as proof for some general nationalistic conspiracy theory.
I think Libertine was on a good path explaining the backgrounds. It's probably generally prefering certain riders to others - especially Valverde, but not only him. And these favourites are usually Spanish.
I suppose there's also more to it than actually backing certain riders with actions in certain races. We can look at the way that a rider gets supported by domestiques, gets freedom to ride for himself, is allowed to take time or win a stage... but then there are probably also little things that happen every day, in communication. You realize another rider is just the favourite of the boss, he gets backed more in the media, gets talked to more, the bosses ask how he is, his wishes seem very important, he gets invited for a private coffee/ dinner, gets called more often (speculation, I have no idea)... and that can build some resentment.
I mean, when Contador and Valverde talk about Mas being their heir - you might say it's because Mas is more consistent, a better time trialer, easier to work with - but of course they are choosing a Spanish rider for this, not a Latin American.
So, the way I understand it now at some point Unzue yelled at Lopez, himself resignated, a bit heated/ annoyed/ angry, something like "Give it up, damn, it's no use!" And Lopez might very well in that moment, very emotional and frustrated have understood that as "what does your placing mean anyway, all we care about is that Mas is still in front". And that was probably the icing on the cake, after all the frustration he had in the months/ years before, the feeling he got already, that they didn't really care about him.
Okay, so about the national conspiracy theory, it's probably not a general totally nationalistic agenda behind, but some favouritism of some Spanish darlings.
And although Lopez reaction was immature, it's also understandable from a human point of view. Him not being at the dinner was probably a good thing for everyone. The real bad aspect about "his" reaction in my eyes is how his partner and his coach/father in law got involved; in these cases I suppose the way an athlete tells the story to his family makes them react like that, and he probably told the story very one-sided and exaggerated...