For me, it doesn't matter why he took the job.
The fact is that in a civilised society, everyone should have access to justice and legal representation, and everyone should have the right to mount a legal challenge through the courts. The only way to ensure that is by supporting access to justice for everyone, even those we consider to be 'undesirable' or unworthy.
Rapists and murderers cannot be convicted with a fair trial, which requires a defence.
I remember when Gareth Peirce was looked down on for representing the Guildford Four. In many people's eyes, they were obviously guilty so why not just lock them up and throw away the key? Why should an appeal even be allowed? People campaigning on their behalf were spat at in the street.
Except they weren't guilty. And without legal representation the miscarriage of justice would never have been addressed.
And even if they had been guilty, they were still entitled to a thorough defence and an appeal based on the evidence, if the UK wants to consider itself a civilised society.
And yes, that includes people who have committed crimes in the past, but are now subject to some other aspect of the law (like the deportations). Everyone has a right to a defence, and appropriate protection under the law, regardless of what their history might be.
Anyone who condemns 'undesirable' people having access to legal representation in the courts is particularly hard of thinking, in my view. One day you might be the undesirable one, fighting for your right to be heard.