"Only when equality is increased within their ingroup, instead of between groups, do advantaged group members accurately perceive it as unharmful." This is why

"Only when equality is increased within their ingroup, instead of between groups, do advantaged group members accurately perceive it as unharmful." This is why it's critical that policies for education, city planning, economic planning etc. all maintain and encourage interaction between classes. If the advantaged are never made aware of the struggle of others, the result is runaway social stratification. Also, these studies are entirely within the US context and so correlate along common historical and geographical lines. Conclusions can't be applied broadly to other societies.