My colleagues' answers here are quite good; you would be wise to read them all. Here's what I have to add.
Sometimes doctors have trouble telling a patient they don't think they can make them happy, for a multitude of reasons. I tell patients who come to see me with tales like yours about other doctors that sometimes what they were told is "doctor-speak" for "I don't know how to do that operation" or "I don't feel comfortable being told how or what to do by a patient who has just done 'research' and isn't interested in my recommendation based on medical school, surgery residency, plastic surgical fellowship, and years of experience" or "You seem unhappy with your life, not your breasts, and giving you bigger breasts will just make you a still-unhappy woman with bigger breasts and a lighter wallet and a new person to blame for your unhappiness." Etc. Some patients are just plain crazy, but we can't tell them that, can we? (And I NEVER say that to someone who I feel is unstable, so don't be offended--I think your question is a very good one and understandably troubling to you or any patient treated this way!) You just have to try to understand why.
Perhaps it is the fact that the "gummy bear" implant is not yet approved by the FDA, and is used by only some plastic surgeons in approved studies (which I believe are now closed). Perhaps it is the fact that textured, form-stable, "gummy bear" implants don't come in round shapes--they are all teardrop-shaped. Perhaps you mean to say 5th generation, cohesive textured silicone gel implants, NOT "gummy bear" implants. Many patients confuse the differing degrees of polydimethylsiloxane cross-linking in present FDA-approved cohesive silicone gel implants with the even-more cross-linked form-stable (you could say "ultra-cohesive") gummy-bear implants, and call all cohesive implants "gummy-bear" implants. That would be incorrect. They are all cohesive, but different kinds of cohesive, and different kinds of implants.
Perhaps it is the fact that placement of textured implants via an axillary incision can be quite difficult if not nearly impossible! The textured surface inhibits sliding, and the axillary incision is small enough (as are periareolar AND normal-size crease (inframammary) incisions) that even the recommended (for textured implants) 5-6cm incision may not "be enough" to easily get these "rough-surface" implants in, and into proper position via this incision location. And the bacteria in the armpit are more commonly "dragged-in" by the textured surface.
There are indeed a few ethical considerations, like "I don't participate in the 'gummy bear' implant study, so I can't do that for you" but that would have been pretty easy to say. Not every good surgeon is a "great communicator," and not every silver-tongued surgeon is a great plastic surgeon--the same goes for "bedside manner."
You really need to see several other ABPS-certified (NOT just "board-certified", but American Board of Plastic Surgery-certified) plastic surgeons ("board-certified cosmetic surgeons" can be Dermatologists, ENT, family practice, or doctors of various training backgrounds and board-certifications. The "American Board of Cosmetic Surgery" is NOT an ABMS member board; the American Board of Plastic Surgery is, and is the only ABMS board that certifies plastic surgeons). Perhaps you can hear good advice and proper explanations!
Your goals ARE important, and should be foremost in every plastic surgeon's mind when providing you with his or her best advice. Please don't be offended when all of your personal research and decision making seems to be disregarded by one or more doctors, but you should also understand that unless you too are a fully-trained, board-certified, experienced plastic surgeon, your own research may be based on false assumptions or incomplete information. It is your surgeon's job to educate you so that you CAN make the ideal choices for YOUR body and YOUR goals. That way, we can best achieve (or at least come as close to as possible) your best and safest result in keeping with your wishes. Good luck!