How do people who become evolution-believing scientists know that a belief which arose in them when they were uninformed, isn't the main reason why they believe today? In other words, could indoctrination, prior to them becoming scientists, ensure that every piece of evidence, every hypothesis, every conclusion they make, is pre-filtered through evolution-tinted spectacles?
The answer to your question is the scientific method itself. The very
point of the scientific method is to
disprove a hypothesis. No scientific theory is "fact." No one who even so much as paid attention in High School science classes thinks that scientific theories are "Fact." They are the best descriptions that fit all of the observed evidence. A hypothesis becomes a theory when it has been tested repeatedly and is never disproven.
Does this mean that all science is flim-flam and just a best guess? No. These theories have been tested and tested and re-tested. Evolution has never been disproven. It has been modified by new data along the way, but the actual mechanism itself has never been disproven. The theory of gravity is just a theory...but you and I are still held to the ground by the force it describes, and actions that depend entirely on our understanding of gravity (space probes, satelite orbits, etc) lend support to the notion that, even if it isn't dead-on, our theory is pretty close to the truth at minimum.
If scientists believed in evolution simply because of indoctrination, they would be failing to use the scientific method itself.
Scientists who believe in evolution were indoctrinated to believe in evolution before they became scientists. And because of that, it is impossible for such scientists to claim they can to be objective about evidence which they use to argue that evolution is true. Or to put it another way, it is impossible for them to demonstrate that they aren't wearing evolution-tinted spectacles every time they weigh up evidence.
Wrong. The highest honors in science go to people who disprove commonly held theories. Newton disproved common theory about gravity. Einstein disproved the notion that newtonian physics were constant. The goal of a scientist is to invalidate common conceptions so that future theory is based more closely on fact.
The mechanism by which EI works is lifelong and repeated exposure to statements which say or imply that Evolution is true. The mechanism starts at a very early age, when there is little to prevent it exerting influence. MI takes many forms: kids nature programmes, tv ads, cartoons, friends taunts, games played, science lessons all the way through school, popular science books, science fiction, natural history programmes,toys, eminent looking scientists saying it's true, early interest hobbies in things scientific, films, magazines, .. and the fact that even the dog in the street knows it. The MI has virtually nothing which opposes it. There is no scientific alternative presented which says our existance is the result of another mechanism (or if there is, it's, relatively speaking, a side issue and not comparable to the mass-influence of the MI - the cogs and gears of which are listed above). Not even religion will necessarily affect it's workings. Many who have a faith: Christian, Buddist, Hindi etc will not consider there to be conflict between their belief and the acceptance that Evolution is true.
Irrelevant. Once an individual reaches the point in their scientific carreer where they participate in research, their goal is in fact to disprove hypotheses, even if they believe the hypothesis to be true (in other words, the testing of the theory is what prevents biased opinion from influencing experimental observation and fact).