1. Medical science is able to explain how deformities are
formed. This is the reason, for example, pregnant mothers shouldn't
smoke.
2. Going back to my original Point (2), if I am born with a
serious physical deformity, the concept of karma will strike me as
grossly unfair. Why should I be made to suffer for the works of my
previous lives -- over which I have no control at all?
3. If Buddhists don't eat animals because of these reasons, is
eating oysters allowed? From what I've read, people can only be
reincarnated into sentient creatures, and lots of shellfish are
believed to be non-sentient.
2. Does it make sense for someone in jail to say, 'why should I
be made to suffer for my burglary last year?' He may even say 'I'm
a different person now! I am no longer the same person as last
year. I'm changed. I am a good man now.' But the fact is the
causality has ripened and yes, he has no control over them.
3. Vegetarianism is not compulsory for Buddhists, however if you
eat meat, the Buddha tells us to avoid eating meat that we have
personally killed, ordered others to kill, or witnessed the killing
(as an example: frozen meat is allowed as it meets these three
criterias of not being killed, etc). Why? Karmic deeds are by
intention - if we have no intention to kill the meat we eat, the
negative karma is not formed. Karmic deeds are of three kinds:
mental, speech, and bodily, but they must be intentional and
volitional - and such volition may be wholesome, unwholesome, or
pure. Even though it may be logically said that we are indirectly
supporting the business of killing, nonetheless no direct karmic
link is involved. That is why Buddha told us to eat meat only when
meeting those three conditions. If you are into Mahayana Buddhism
and wish to cultivate great compassion, then vegetarianism is
highly recommended.
But to answer your question: oysters are sentient animals and so
we should avoid eating those that are cooked alive. Likewise, try
to avoid eating seafood that are ordered fresh since it means you
have ordered them to be killed.