This seems like a great opportunity to change people's views of what their "opposition" looks like. I wouldn't worry about convincing them - you won't. Instead, your goal should be to show that the other side is reasonable, if you choose to speak up again. You do this by recognizing legitimate concerns they have and clearly stating why you don't agree with all of their concerns. By the the topics, this might look something like;

Euthanasia: A legitimate concern is that euthanasia may occur without the consent of the patient if it is widespread. The response is that, while unlikely, that may occur, and it is legitimate to worry about that. Our worry about that does not, however, give us the right to put people through long, painful deaths. The right of the individual not to suffer in this way should be recognized, with careful legal protections so that others do not have their rights trampled on. With this audience, you'll likely have to defend the concept of rights, which they will claim have a metaphysical origin. This is a red herring - everyone agrees that rights are a useful concept, if only that. Focusing on avoiding real human suffering is a powerful way of showing that your position is reasonable. (Assuming this is your position, of course)

Abortion: Similarly, abortion is an issue of compassion. While many people believe abortion is wrong "in a vacuum", that does not imply that we should also believe that women give up their right to bodily sovereignty when they have sex. Abortions happen for many reasons, but are usually aimed at avoiding great harm to the mother. Sometimes that harm would be the end of the mother's education, and a corresponding lifetime of economic challenges, and sometimes that harm is the real bodily changes and dangers that pregnancy brings with it. Admitting that this may be a complex issue, but arguing that the right to personal autonomy is incredibly important and deserves greater weight than simplistic " pro-life" arguments give would be my take.

Biotechnology: This one is tough without knowing the specific topic. It is easy to once again point out that there are competing interests here, but I'd have to judge this from what is actually discussed. If I were you, I would spend some time reading the academic literature on these topics before going. At the very least, you'll be prepared for whatever the arguments end up being.