"He that would make his own liberty secure must guard even his enemy from oppression; for if he violates this duty he establishes a precedent that will reach to himself." ~ Thomas Paine, 1795
That's the same principle that led then-lawyer-and-revolutionary John Adams to vigorously defend five British soldiers (of the hated occupying army) accused of one of the most notorious crimes of the revolutionary period: the 1770 murder of five colonists in Boston as part of the so-called Boston Massacre. As the ACLU explained, no lawyers were willing to represent the soldiers because "of the virulent anti-British sentiment in Boston" and "Adams later wrote that he risked infamy and even death, and incurred much popular suspicion and prejudice."
Ultimately, Adams called his defense of these soldiers "one of the most gallant, generous, manly and disinterested actions of my whole life, and one of the best pieces of service I ever rendered my country." That's because Adams understood what Paine understood: if you permit the government to trample upon the basic rights of those whom you hate, then you're permitting the government to trample upon those rights in general, for everyone.
This is not a platitude they were invoking but an undeniable historical truth. Governments know that their best opportunity to institutionalize rights violations is when they can most easily manipulate the public into acquiescing to them by stoking public emotions of contempt against the individual target. For the reasons Paine and Adams explained, it is exactly in such cases - when public rage finds its most intense expression - when it is necessary to be most vigilant in defense of those rights.
http://www.guardian.co.uk/commentisfree/2013/apr/29/tsarnaev-right-to-counsel-denied