I agree that condos share quite a lot in common with a gated community - and may even prove to be a near-universal second choice for those who wish to live in gated communities.
But they are far less destructive. The footprint is much smaller: you can fit in one city block the same number of people that would cover vast expanses of land in a gated community. And the condo encourages and increases density, which makes living together in cities and sharing the burden of municipal services more affordable for everyone.
Also, the psychological impact is less. Walking by a condo building you wouldn't get past the front desk in is not nearly as striking as driving along a fence for kilometres, with obscene wealth on one side and average existence on the other.