Your view of a ghetto is pretty unique. Have you been to a ghetto recently? Anyway, see definition #4 in answer to your question as to why Trump’s use of the term in reference to black people is offensive.
noun, plural ghettos, ghettoes.
- a section of a city, especially a thickly populated slum area, inhabited predominantly by members of an ethnic or other minority group,often as a result of social or economic restrictions, pressures, or hardships.
2. (formerly, in most European countries) a section of a city in which allJews were required to live.
3. a section predominantly inhabited by Jews.
4. any mode of living, working, etc., that results from stereotyping or biased treatment:
job ghettos for women; ghettos for the elderly.