Partly this is because Federal Conference Committee itself contains good Liberals, who I am confident will have been sensitive to the views of party members when dealing with the police over security arrangements.
Secondly, I don't really think it unduly onerous that people attending conference should be able to show that they are who they say they are. Nor that people who are likely to be a serious security risk should be excluded.
But also, in general I agree with late Conor Cruise O'Brien's arguments down the years that liberals can fail to take the terrorist threat seriously and be a bit cavalier about security issues. At the same time I suspect that if there were to be a serious incident at conference leading to loss of life, there would be few people lining up to defend FCC and the police, and many people asking how they allowed this to happen.
After the Brighton bombing at the Conservative party conference in 1984, and Mrs Thatcher's narrow escape, the Provisional IRA said:
Today we were unlucky, but remember we only have to be lucky once. You will have to be lucky always.
It doesn't seem unreasonable to think that as part of a government taking difficult and controversial decisions at home and abroad, the Liberal Democrats might find their conference being targeted and should take suitable steps to protect those attending.
It's perhaps worth adding that in the heyday of Liberalism in Victorian and Edwardian times, much effort was expended by all political parties to stop opponents disrupting their meetings.