A competitive market should improve the quality of planes: no one should buy a Boeing if there is a viable alternative. Allowing the merger reduced competition.

We really shouldn't blame deregulation (in the sense of reducing the barrier of entry to airline markets). Lower airline ticket prices (Europe is a case in point) is better for everyone. And if quality were indeed lower, then another company should be able to swoop in and capture a higher tier quality market if there are people willing to pay for it (like first class, or business class)

Lack of anti-trust enforcement in the aerospace manufacturing industry is entirely orthogonal and hurts plane safety.