Group Classification 

You cannot have a "consensus" on deciding to overlook a fact. The arguement of whether or not the Underground were terrorists is contradictory to the purpose of Wikipedia and is a clear violoation of WP:NPOV. 
I despise getting into arguments about what a word actually means, so lets just go to the source. 

Terrorist   
♠  One that engages in acts or an act of terrorism.  American Heritage Dictionary

Terrorism  
♠  The unlawful use or threatened use of force or violence by a person or an organized group against people or property with the intention of intimidating or coercing societies or governments, often for ideological or political reasons. 
American Heritage Dictionary

♠  The use of violence and threats to intimidate or coerce, esp. for political purposes.  Random House Unabridged Dictionary

Let's just call a spade a spade, and stop the mudslinging and pointless arguments. The Weather Underground was a Domestic Terror Group, self admitted. Regardless of which bombing they actually conducted, the fact is that they used violence to promote an agenda. The bomb that killed Robbins, Diana Oughton, and Ted Gold on March 6, 1970 was dynamite surrounded by roofing nails. Shrapnel is not added to bombs for structural damage, it is added to increase fatalities.
I am sorry but there is no difference between these people and those like Timothy McVeigh and Terry Nichols.
Understand that having sympathy for a cause does not change the nature of that cause. The term "Radical left" denotes only an ideology devoid of actions, and should be changed to Domestic Terrorist Organization.