Brixton has an undeserved reputation for being a
violent,
dangerous place to be, which although justified a few years ago, is no longer strictly valid. Many places in
London are much less fun to be in than Brixton (
Lewisham,
Manor Park,
Kennington etc).
Brixton is now a relatively safe place to be, and is ceratinly a fun place to be; it is full of bars and clubs. The most well known of these are Mass (converted church, often used for somewhat underground club nights), The fridge (ex-cinema, top venue for hard dance), Dogstar, Club 414, and the Brixton Academy (Old theatre, used for big-ish rock concerts).
It is true that brixton has a deserved reputation for obvious drug use. This is partly due to the number of hard dance clubs, and partly because the local police have a policy of not arresting people for smoking cannabis. However, drug use does not, in itself, make for a dangerous area, and I know that I would rather be in Brixton at 2am than Lewisham.