It's right to be concerned about conspicuous consumption, not only for its own sake but also because there is a connection between consumerism and poverty. However, the connection is not simple. An end to conspicuous consumption among the rich would not automatically create opportunity for the poor; something more is needed.
Concerns about what we now call "conspicuous consumption" are literally as old as history. The first written legal code in Greece forbade women from wearing gold jewelry or embroidered robes in public (unless they were registered prostitutes). The founder of the Ming dynasty, adding to a large body of sumptuary laws dating to the 3rd century B.C., restricted the size of graves and mausoleums. Elizabeth I, issuing a very long and elaborate list of who was allowed to wear what, warned that wasteful consumption would bring about "the manifest decay of the whole realm."
These historic concerns about the ostentatious use of wealth can lead us to several important insights. One is that Thorstein Veblen's atheistic theories about capitalism, from which we get the phrase "conspicuous consumption," are wrong. He thought this was a new problem, or at least a newly expanded problem, created by the increased efficiency of capitalism. But the more we study history, the more we appreciate the ubiquity, and even the monotony, of human sin. Genesis 1-3 provides the most empirically verifiable scientific explanation of economic behavior.
The next thing to notice is that sumptuary laws restricting ostentatious consumption, while they are a common feature in history, were virtually never advocated as a way to lift up the poor until recently. Quite the contrary; one of the key purposes of these laws was often to reinforce social hierarchies. Everyone's consumption was limited, but the poor were even more restricted than the elites. Those restrictions on graves in the Ming dynasty allowed you to have a larger grave the higher you were on the social ladder; ditto for Elizabeth's restrictions on dress. The idea that you can lift up the poor by tearing down the rich was around, but it didn't make much headway until after the rise to prominence of atheistic economic theories in the 19th century.
Neither approach serves the poor. The old way explicitly suppressed the poor, restricting their consumption even more than that of the rich, and thus reinforcing the boundaries that kept them trapped in poverty. The new way tries to help the poor, but it fails because it's materialistic.
The dominant idea today is that "conspicuous consumption" directly oppresses the poor; the money that was spent on frivolous luxuries should have been redistributed to those in need. This assumes that what the poor need most is money, and that we can create justice and opportunity by moving money around.
This approach has been a complete disaster, not for the rich but precisely for the poor. The rich actually like it; they can pay high taxes to support the welfare state and then feel like they've done all they need to do for the poor. Meanwhile, they actually keep the poor trapped in an alternate social world where the relational structures of family and work have broken down. The poor cannot rise, not primarily because they lack money, but because they lack access to things money can't buy — above all, stable family and work relationships.
The old approach to conspicuous consumption, while it was wedded to strict social hierarchies that we must reject, at least began with moral virtue. It grew from two basic ideas: ostentatious or frivolous consumption of wealth is inimical to moral virtue, and moral virtue is a matter of urgent public concern. There is no reason we can't recover these two vital ideas while leaving behind the paternalistic stratification they were once associated with.
When people — any people, really, but of course the rich are more noticeable — use wealth ostentatiously or frivolously, they are reinforcing a poisonous materialism in the public square. The good life, they are saying, the life you want, is a life of gratifying your desires. This materialistic approach to life is a primary cause of poverty. It stands behind unjust and exploitative social systems that deny opportunity to the poor, and it also stands behind dysfunctional behavior among the poor themselves.
To overcome poverty, what we primarily need is to restore a public understanding that the good life is the moral life, a life of contributing positively to the needs of others rather than consuming resources for ourselves. This involves helping the poor reconstruct right behaviors in their own lives. But it also involves opposing the evils of the powerful — not only the direct injustices they commit against the poor when they destroy opportunity, but also their public manifestation of the materialistic approach to life.
Tearing down mansions in the countryside won't build affordable housing in the inner city. But exposing the materialism that builds the mansions is essential to a social order in which the poor will have the opportunity they need and deserve.