I know a handful of sports fans who, as persons of color, have patiently explained to me how they were raised with a distaste for Boston as a city because of the history of its fans a racist people. The city, I believe, has come a long way from the days of Russell and the bussing issues, but there is a fundamental and underlying element of racism that is inherent in such a white, "educated," and OLD city. It is not just Jermain Oneal or Garnett saying that Boston is racist, its their mentors telling them and their mentors telling them because Boston, at least, WAS racist and VERY unfair to its prominent black athletes from an early time.
So no, I do not think the shamrock turns players away, but I think the historically prominent white presence in Boston has, however fair, unfair, accurate, or inaccurate it may be now.