I've just heard the sad news that Peter Tatchell  has stood down as a Green Party parliamentary candidate after brain injuries caused by beatings which have left him unable to campaign effectively.
The brain damage is the result of assaults on him by Robert Mugabe's henchmen in 2001 and by neo-Nazis during an attempted Gay Pride parade in Moscow in 2007.
In a statement announcing his decision, he said:
The injuries don't stop me from campaigning but I am slower, make more mistakes, get tired easily and take longer to do things. My memory, concentration, balance and co-ordination have been adversely affected. I can't campaign at the pace I used to.
I last heard Peter speak at a debate we hosted on constitutional reform at this year's Labour conference. He was as eloquent and persuasive as ever, but visibly frustrated by the errors he made.
His fate reflects what one could call the activist's dilemma. How to challenge authority and abuse without impairing your ability to do so in the future?
In response to such concerns, Tatchell insists: je ne regrette rien.
Here is his admirable justification::
Getting a thrashing and brain injuries was not what I had expected or wanted. But I was aware of the risks. Taking risks is sometimes necessary, in order to challenge injustice. My beatings had the positive effect of helping draw international attention to the violent, repressive nature of the Russian and Zimbabwean regimes. I'm glad of that.
My physical inconveniences are nothing by comparison to the far worse beatings inflicted on human rights defenders in countries like Russia, Iran, Zimbabwe, Saudi Arabia, Colombia, Sudan and Burma. These heroic activists often end up jailed or dead. I count myself lucky.
Tatchell is one of the few figures on the left who since September 11 has managed to twin a powerful critique of US foreign policy with an effective critique of Islamism. His campaigning reflects the truth that human rights are meaningless unless universally defended. Let us hope his decision aids his recovery.