Satire
Not only is Babbitt satire; it's considered one of the best American satires of the 20th century. Some people might read the book and think of it as a realistic or even tragic account of a man who just wants to make money and feel young forever, but in the end, there's little doubt among critics that Lewis is holding Babbitt and his conservative buddies up for us to mock.
Lewis makes Babbitt's hypocrisy easy to see by showing just how contradictory some of his thoughts are, especially when it comes to being "moral" in his business practices. Babbitt constantly cheats people out of money, but he's also the first to pounce on someone else whom he suspects of being dishonest.
Ultimately, Lewis isn't necessarily telling us that we should all become socialists. But he definitely wants to point out some of the biggest flaws of free market capitalism and the type of person who tends to support it: repressed and deeply unhappy middle-aged men, in Lewis' (not so) humble opinion.