As coin has two sides this problem too has 2 shades.
i'm giving only hints with those form ur debate
1. increase in slum areas
2. due to increase in populationĀ  city expands. this increases budget resulting economic decline
3. overcrowdind
4. no proper housing due to increase in population
5. unemployment
6. transport shortage
7 shortage of water
8. sewerage problems
9. waste disposal (there will be no place)
10.increase of crimes to earn bread and butter
11. pollution.
expand these causes one by oneĀ  with examples. u'll get enough debate.