>Each conscious being is irreplaceable.

Right, that's my point - the conscious being of your childhood is not replaceable with you now. You are a clone of your dead childhood self. That's fine for you, the clone. But who's interested in getting a 30-year-old clone? And the many consciousnesses that flower and die every few decades, will be replaced with the single continuation of a single generation that stumbles into immortality.

>I think that's a sedative, like all religions

I'm not Buddhist, but your critique extends to yourself. If you take one step back to look at an even broader picture, by replacing religion with ideology, you've just reinvented postmodernism. Viz: "Transhumanism, sedative, like all ideologies." So you either stick with modernism (that transhumanism is the one, special ideology immune from humanity's tragic need to self-sedate), or dive into the void (which really is just an ocean of sedatives swirling together, I've swum deep and I promise it's ideology all the way down).

Maybe we're not self-sedating at all, and we can talk to a pharmacist who isn't just us. It's hard to say anything about reality when the only thing you know is that you're high af all the time.

>I've been alive for 30 years - not much, I admit, but I still feel as much like me as in the first day that I can remember.

Every day the same sun rises, yet it's a different day. You aren't the sun, you're the day.

Imagine droplets of water trapped in a cup, then poured back into the ocean. Water is consciousness, your mind is the cup. 

Each century, the day ends, but your family continues. Every few centuries your family falls apart, but your community thrives. Each millenium your community is ravaged, but your nation lives. 

We could go on, to the species, the community of all conscious beings, etc etc. Where you place the self along this line is historically variable. You place it with the continuity of the ego. I place it with my family. There are a zillion answers to this question. Buddhism would say the attempt to answer this question is itself the problem. But I'm not Buddhist.

To meaningfully debate this, we'd have to find out what consciousness is. The academy already moves at a snail pace as science continues to progress one funeral at a time, awaiting the death of precious selves whose lives already had negative value decades ago. Imagine if their reign extended infinitely. But for the grace of Death might we soon unlock Immortality.