Why is there so much racism in Australia against the Lebanese?
Well, for one 37% Lebanese-Australians are Muslims. All Muslim groups have been seeing increased discrimination since 9/11.
A lot of the racism against Lebanese people in Australia however dates to before 9/11. The Lebanese got a bad reputation after the 2000 Sydney gang rapes where 9 Lebanese-Australian youths gang raped several Anglo-Australian women in multiple attacks over the course of 2 months.
They said things to the victims like "You deserve it because you're an Australian".
This type of thing tends to reinforce and rekindle old-time racist hysteria. Then a year after those gang rapes, 9/11 happened.
In 2005 some Lebanese-Australian youths got into a fight with lifeguards in Cronulla which eventually lead to the 2005 Cronulla riots also known as the Sydney Race Riots.
Now the main thing contributing to anti-Lebanese paranoia is probably ISIS and radical Islam at large. In 2014 there was an ISIS plot to behead random person in Sydney.
The odd thing is that most Australians, I think, view Lebanese people as Muslims despite the fact that the majority of Lebanese-Australians are Christian. Lebanon itself had a Christian majority before 1980. Hatred often doesn't follow real logic, even if you thought with this type of logic:
Lots of Muslims are terrorists.
Therefore hate muslims
It makes little sense because only a minority of Lebanese Australians are Muslim.
Some of it is racial as well. Australia has a large proportion of people that do not want non-white immigrants, or want less non-white immigrants than white immigrants because they see a threat to their demographic majority. Even in the late 80s and early 90s mainstream party platforms had things like One Australia policy. Fringe politicians like Pauline Hanson and Stephanie Bannister still get a large following in more conservative areas.