John Adams defended eight British soldiers involved in the Boston massacre, of which only two were ultimately convicted. In the proceedings he referred to the mob (full of the future revolutionary elements he would later rely on) as:
a motley rabble of saucy boys, negroes, and molattoes, Irish teagues and outlandish jack tarrs [i.e. sailors].
He later validated his defense of the soldiers as a blind understanding of their natural liberties:
The Part I took in Defence of Cptn. Preston and the Soldiers, procured me Anxiety, and Obloquy enough. It was, however, 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.
I have two questions from this: (1) was his stated rationale as pure as he would have us believe, and (2) did it alienate his fellow revolutionaries?
Yes; and sort of. David McCullough does a good job reviewing this incident in his biography John Adams, which I recommend reading if you're interested in Adams.
John Adams was emphatically devoted to justice and the law, and would have believed the soldiers deserved a fair trial - this sentiment is borne out in his many, many letters and writings throughout the years, so his stated rationale for defending the soldiers is not hard to believe. It also wasn't his sentiment alone - the whole point of the trials were to be as fair as possible to give the British govt. no cause to retaliate should the soldiers be found guilty.
As I recall Adams did indeed suffer a blow to his public esteem when he accepted the appointment (which tore at him, as he was intensely concerned with others' opinion of him), though by the end of the trial he had more than recovered. Basically, people were quite impressed with how well he had done his job, despite having defended British soldiers accused of murder, and the passion and logic with which he argued their case. Adams was actually elected to the state legislature a few months after the trials ended, so clearly he was well-respected after the fact.
Edit: Realized you asked about opinions of Adams as a Revolutionary, and not explicitly his status as an attorney in MA during the trials. As far as I know, no, he wasn't doubted as a revolutionary due to his defense of the British soldiers. He was generally seen as one of the more passionate supporters of the Revolution, particularly in Congress, and was one of the driving forces behind the movement to formally declare independence from England. Even some of his political enemies (other members of Congress, their names escape me), would sometimes recall that despite a disagreement or other character flaws they saw in him, they found Adams ultimately to be a true patriot.