If you don't live around people who are less fortunate than you, how can you understand their plight and their point of view? Handing out a few bucks to a homeless guy or cutting a check to a non-profit doesn't create any substantial understanding of the issue.
Obviously there will be opposition to this in the US since people want to live with other people in the same socio-economic strata as themselves. Other reasons: 1) I don't want my property price to depreciate 2) I don't want to live next to "da hood" etc. Until people have a drastic change in attitude this will be ongoing. The article touches on this a bit (section 8 vouchers) but why can't we have neighborhoods with multiple levels of housing options encouraging people with mixed incomes to be around each other.