If both of parties involved in a relationship are not having the same feeling, there's no point in going ahead. Even if you marry under such circumstances, things will come out to be disastrous in the long run.
From your description, what is evident is that, your boyfriend is giving you lame excuses and wants to wash his hands off from the responsibility of marrying you. This is hurting, resentful. But that is the bitter truth.
From your words again, we didn't find anything unusual from your parent's side. Rather they sound to be more reasonable than your boyfriend. Where is the issue of killing coming into the picture? Your parents are only concerned about your future, as their experience can see things what you cannot.
Your boyfriend is only taking advantage of your innocence and scaring you with some funny ideas.
For you, I understand, what you are going through. Hence, the best way to test the water is allowing some time to pass through. That will at least test the attitude of your boyfriend.
On the other hand, let me explain, what will happen, even if your boyfriend gets convinced by some or other way. Your married life will be hell.
If you are still unable to come out of it, ask your boyfriend not to contact you for some days. Though it will be really tough from your side, that is the only way you can find out, if your boyfriend needs you anymore.
Continue this for at least a month. Once you can see things with clarity, making the right decision will become easier for you. But forget the idea of convincing anyone for marriage, Neither your parents, nor your boyfriend needs to be convinced. They have already made their decisions. It is you who needs to rethink the entire issue and take the right step towards your life.