We have the ELF in Britain, and , unlike in the US, they have actually injured people (the manager of a commercial animal testing lab in Huntingdon). Most of their attacks consist of vandalism and destruction, rather than attacks on people.
They are pretty much condemmed by the vast majority of environmental protestors who use non-violent methods to make their protest known.
Non violent protest is still a right in both the UK and USA.
We have had experience of violent terrorism in the UK, and it is in quite a different league to the ELF. One former leader of an IRA unit is now the education minister for Northern Ireland. It seems that bombs do get you somewhere.