Actually, Roger Hallam is quite content with being sent to prison. It is part of his plan to overthrow the government and pave the way for one that will take the actions to combat climate change that he considers imperative.
In his booklet Common Sense in the 21st Century he set on how he sees the revolution developing:
“If they [the government] opt to repress the protestors, they risk a backfiring effect. This is where more people come onto the street in response to the sacrifices of those the authorities have taken off the street. In situations of intense political drama people forget their fear and decide to stand by those who are sacrificing themselves for the common good.”
In other words, he sees the movement for revolution developing as more and more people are drawn into it through being appalled by those (like him) who have “sacrificed themselves for the common good” being sent to jail.
It doesn’t seem to be working according to his plan. Most people, even in “climate justice” activist circles, seem indifferent to his fate.