There are two policies I advocate to get tough on the causes of riots.
a) Legalize drugs. Gang culture thrives when stuff people want (alcohol, lotteries, drugs...) is made illegal.
b) Get serious about reducing long-term unemployment. It disengages people from society (even, or especially, young peoploe facing the prospect of it.). There are far too few jobs now for unskilled labour. The way to fix this is to subsidize jobs. We need a negative income tax for low paid workers.
(a) is almost unanimously agreed among the sort of people who like to talk about this stuff without actually being responsible for it (like me). I reconsidered it last year when a colleague died in a fall after taking cocaine, leaving a wife and young child. I would expect legalizing drugs to lead to more people taking them. Against this, the composition would be much better controlled. We accept the health risks of alcohol: anything which is not clearly more dangerous should be legal (I suspect that cocaine would not qualify: this is a question to be determined scientifically).
(b) is rather more daring. I'll write some more about it.