All of those are currently illegal.
I'm not sure what Twitter should do - include an abuse button that sends reports to a Twitter team who then report people to the relevant police? Or who then collect evidence in case the police contact Twitter (with suitable legal documentation)?
People do go to jail in the UK for making stupid comments on the Internet.
Here's an English 'troll' who made threats against US schools: (http://www.bbc.co.uk/news/uk-england-22813326)
Being able to report illegal content seems like a reasonable request. Being able to report content that breaks the ToS / AUP seems like a reasonable request. Protecting the free speech rights of people who are saying unpopular (but not illegal nor ToS violating) things shouldn't be a barrier to protecting people from harm.
I guess they might want to have some kind of transparency report to show how much stuff gets taken down, how often, and what kind of thing it is.