2) The delta in material situation between India and US is far higher than the delta between US and and Singapore. Westerners moving to Singapore aren't escaping grinding poverty.
3) There's a large Indian community in Singapore (indeed the very name of the country is in an Indian language) and if you're going to compare Indians moving to the US to another group moving to Singapore (well, perhaps not moving -- they've been there for a long time), this is probably the right comparison to make. I don't see a problem with multi-ethnic states, as long as everyone lives by the same basic laws. I'd still think I would find it acceptable even if the cultures were completely isolated from rest of the country, e.g., Amish in the US, as long as -- again -- they lived by the same laws.
4) I did state elsewhere that I think in terms of immigration policies, Singapore may be "superior" to the US. I strongly believe in immigration as primary human right: everyone should have the right to move wherever they please (with only exception being due to basic economic condition -- a mostly theoretical concern, as usually countries with greatest population densities and largest immigrant population tend to be more prosperous), whether this is the right choice for others is a personal matter (something I can speak out against, but have no right to deny).