More than 25 years after its release, David Lynch’s groundbreaking Blue Velvet (1986) has lost very little of its ability to shock and disturb. Steve Head and David Kleiler revisit this ’80s classic, and shed light on Lynch’s unique film language.
Episode No. 11: Blue Velvet (1986)

I disagree with the conclusion that Mr. Kleiler has drawn concerning the film’s ending. I do not think it’s in the least bit ironic, or that Lynch intended it to be interpreted that way. I believe Lynch in this instance is being very much a literalist here, and wants us to see/feel that a certain superior worldview has triumphed here over an inferior one, that of the blue sky/solar robins prevailing both physically and morally over the subterranean/lunar world of the Franks and Bens.
I would also add that MacLachlan’s and Dern’s characters inhabit another world, separate and distinct from the one that Hopper and Stockwell do, which for them means that even though they may be aware of the corruption lying beneath the apparent surface of things, they are, and forever will be, separate and apart from it.
Finally, I think Blue Velvet can be seen as a dry run for the themes that Lynch would later go on to expand upon more vividly in Twin Peaks.