I don't understand why the aviation sector is no nationalist and protective when you compare too other sectors that have had multinational companies for decades! I mean just imagine the benefits of having a multinational airline with bases all around the globe!
Simple, there is a lot of money and jobs involved.
Imagine country X. Country X has a massive airline called HIJ. HIJ is based out of a massive airport, ABC. ABC airport is one of the biggest employers in country X if you include all the functions of the airport (airline emloyees, baggage handlers, shopkeepers, taxidrivers etc). It is a massive contributor to the X'ish economy, both directly but also indirectly, by offering direct connections through the national airline, HIJ, which in turn help X'ish corporations connect with the world, in turn making more money, employing more people and paying more taxes.
Now imagine if HIJ goes bust because the foreign low-cost airline Moravian out-competes it. Would Moravian ever place as many aircraft and employees in ABC as HIJ did? Not likely. There will ultimately be a reduction of flights, making country X less accessible to the world, which would probably harm X'ish corporations and jobs in the long term. And if the economy takes a turn for the worse, Moravian might not feel as obliged to keep running unprofitable flights as HIJ would have been. Moravian and it's employees might not even pay taxes in the country X.
On top of that, there are issues on safety, work regulations and ethics, like Varsity1 touches on.
I'm not saying I disagree with you, but it is a fact that many countries see need a reliable air-service with all the money and jobs involved.