As long as he doesn't dirty his hands.
But he should be arrested as an instigator once violence breaks out...and it will.
Within the last couple of weeks, a court in the United Kingdom acquitted protesters who had damaged a coal burning electrical power plant. Their defense ... necessity - that it's acceptable to commit a small crime to stop a larger harm or for the common good. The trial had a number of environmental "experts" (all from the left, of course, including one from the USA) testifying about how many residents near the plant would be killed by pollution, how many would be displaced by global warming, etc. etc. etc.
As a side note, "necessity" is a recognized defense in the US as well. For example, you are lost in the woods in the the middle of winter and come upon an uninhabited cabin and break in to save your life. Necessity is a defense against a charge of burglary. What Al Gore seems to be saying is that he would like to see necessity extended to cover sabotage to "environmentally harmful" facilities here. In other words, the ELF burns down a GMC Hummer dealership and is acquitted because they saved future lives.
Jack