We don't know what the true impact on society will be if medical immortality is discovered -- but the thing is that the current impact on society of its lack is about 60 million deaths per year. A death toll of the scale of World War 2, every single year.

Can I condone such a death toll for reasons as uncertain as the fear of the possible formation of a immortal super-elite which will lead the rest of humanity to misery, or of the fear of overpopulation bringing misery, or of dictators lasting a bit longer in power than they otherwise would?

No, I can't condone it. Yes, I'm sure lots of problems will arise if medical immortality is discovered. But as a rough calculation none of those problems is nearly certain enough to justify 60 million deaths per year in return. Your own calculations of this may be different.

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As a sidenote your concept of just the elite becoming immortal isn't an automatic dystopia either. If anything, I think that might make them a bit more responsible in evaluating the long-term consequences of their policies.