--- Having Shepard kill himself, or have Hackett fire on his position, wouldn't be a selfish suicide, it would be a selfless suicide. He would remain true to himself, and not impose his will on any other lifeforms (transforming every living thing or even controlling the reapers. They have Free Will (or at least they did before the Catalyst) and you can't take that away, that's worse than death. Just kill them

He would put his faith in all the friends and allies that he'd recruited. Especially by destroying the Catalyst, he would give real hope to the Galaxy: without the Catalyst, the paradigm would be shifted, and maybe the cycles wouldn't repeat again.
--- Synthesis is not for the good of all life. It's not for the good of anyone. If what I am is abhorent or not viable, and you change me to be something acceptable or viable, then I am dead, and some new... THING is walking around wearing my face. I am me, and remaining myself is the sacred right of every living thing.
--- Synthesis was first brought up as a topic not verbally, but surprisingly during the Vision that Shepard had from the beacon on Eden Prime in ME1's first few moments. Among flashes of Ilos, Teeth, ruined cities... he sees what looks like meat with circuitry on it. It was utterly disgusting. To think that is preferable to death is to abhor one's very nature.
--- Many, MANY times, the game has shown us the theme of sacrifice, but only to stand up for what one BELIEVES, not for mere scrabbling survival. Ashley Williams (Or Kaiden for those of you who banged Ashley and then felt guilty) died insisting that I made the right call. They died not for survival, but for their oaths and the duty they were proud to do.
Wrex died (if you sucked at talking) taking a stand to restore his people, not only physically, but to give them their PURPOSE back.
Thane fought for me and died, knowing that he was sick and would be at a disadvantage, because we were bros.
Kal'Reegar and his men died heroically in an EMAIL, saving turians, because they were proud to serve because I did the same for them once.
Mordin died to fix a mistake he made, and also for personal redemption. He didn't like what he'd become, and he would do whatever it took to return to his happy, singing self, even if it would be only for a few seconds.
Lt. Victus died because he was a soldier, sure, but also because the way that his prople planted the bomb on Tuchanka was reprehensible. If it had gone off, who would have known anything? Tuchanka is a nuclear wasteland! **** blows up there all the time! And while REAPERS are wandering around on it? PLEASE!
Legion died to give his people INDIVIDUALITY. It was totally unnecessary, they would have "survived" just fine without a sense of self. But he did it because he knew what it was to be a person, not just a machine, and it was more important to give that gift to others.
EVERY SINGLE CHARACTER in Mass Effect 2 goes on a Suicide Mission with Shepard. None of them expect to come back. They don't just go because they want to stop the collectors; through the Loyalty Missions you forge a bond, and, as Hackett tells you, they go with you because you are Shepard, and they trust you, and that's worth risking your life for.
In the End, Shepard's "Sacrifices" are all a betrayal of who he is. A Paragon would never pick Synthesis or Control, or Destroy if it meant the death of BILLIONS of Geth and his own friend EDI. A Renegade would never pick Synthesis or Control, and he wouldn't pick Destroy simply because a Renegade wouldn't do anything that little ****** suggested. It just SEEMS to be bad writing (though I admit that it COULD be good writing that was executed in a very poor, very slapdash, very rushed, very craptastic way.) Which brings me to...
--- Indoctrination Theory. If this is true, and Synthesis and Control are losing options, and Destroy with a high EMS results in Shep waking up and the fight still going on, we're really not told this... After the Credits, instead of "I'm Buzz Aldrin, buy DLC," if we had seen a short video that confirmed these things, then the 3 ending "choices" would have been a BREATHTAKING mind****.
After picking Control, if I'd seen Shepard's face all screwed up like the Illusive Man and Saren, and him gunning down his OWN TEAMMATES, I'd have gasped, fell back on the floor, and been like "MY GOD, WHAT DID I DO!?!?!?"
If after picking Synthesis, we would see Shepard's half-mechanical body wired into some machinery, and then it pulls back and we see he's part of a new Reaper that proceeds to vaporize the victory fleet that we'd worked SO hard to assemble, and the last thing we see is this new reaper destroy the Normandy, and Joker's lifeless corpse floating in the vaccuum, we'd get a sinking sickness in our stomachs, but it would be a GOOD one; we'd see a sad, horiffic, poignant ending about the soul and free will and all that ****, but we'd know we could reload and try again.
And of course, if after picking Destroy on a high EMS file, if we see Shepard wake up, and a Edi helps him to his feet (to confirm that it was a mind**** and not real) and then he grabs a gun, turns to face the conduit, and then the game just ENDS, we'd all not only accept and even ENJOY the ending, we'd all be ready to BUY MORE DLC AND GAMES!
--- As it stands, I won't be buying more games from BioWare, for the time being, at least.. This isn't a boycott or anything, I just don't trust them to deliver what I like anymore. It's like when Taco Bell started CAKING Cilantro into their Crunch Wrap Supremes. Or when my local pizza place started using Fennel in the sauce (YUCK!.) It used to be great, now I don't enjoy it, and I'm sad, because I wanted more of what I liked and thought I could keep getting.