In his famous 1974 commencement address at Caltech, Richard Feynman
provided an inspiring counterexample of how science ought to be practiced.
He began by warning against self-deception, the original sin of science,
saying that "the first principle is that you must not fool yourself, and
you are the easiest person to fool."  To avoid self-deception scientists
must bend over backward to report data that cast doubt on their theories.
Feynman applied this principle specifically to scientists who talk to the
public:

    I would like to add something that's not essential to the science, but
    something I kind of believe, which is that you should not fool the
    laymen when you're talking as a scientist. . . . I'm talking about a
    specific, extra type of integrity that is not lying, but bending over
    backwards to show how you're maybe wrong, [an integrity] that you ought
    to have when acting as a scientist. And this is our responsibility as
    scientists, certainly to other scientists, and I think to laymen.

(The above summary of Feynman's views on the challenge of objectivity in
science is taken from Phillip Johnson's afterward in "Mere Creation",
W.A. Dembski ed., InterVarsity Press, 1998.)

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Other interesting quotes:

"Everybody is entitled to their own opinion, but they're
not entitled to their own facts. The data is the data."

-- Dr. Maria Spiropulu, NYT Sept. 30, 2003.

Apparently this originated earlier, with Sen. Daniel Patrick Moynihan (c
1982-1989):

"Everyone is entitled to his own opinion, but not to his own facts."

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"Marshall taught us that what was right was more important than who was
right."

From one of the testimonials at Marshall Rosenbluth's 75th birthday
celebration, quoted by Pat Diamond in the UCSD press release for
Rosenbluth's obituary, who died Sept. 23, 2003.