I would agree with you re: people who are citizens of only one country. Leaving a natural-born citizen stateless is unacceptable, and the law says that in most countries (including the UK).
I think the situation is different for people who have multiple citizenships (of which I am one). We absolutely do have conditional privilege. I can leave the UK, go to one of my other countries or to an EU-country, and the UK will never have any type of jurisdiction over me. I see my situation as very different than that of people who are UK-only citizens and have no choice but to rely on the British government. Dual citizenship is sometimes problematic, and Drobiazko's citizenship is evidence of that.
Shamima Begum is an interesting case because she was technically entitled to Bangladeshi citizenship. Those arguing to strip her of her natural-born British citizenship made the argument that she would not be stateless. It was not a clear-cut case, though I lean toward your / Jacob Rees-Mogg's view that she would've been practically stateless. The Drobiazko situation is not ambiguous. She is a Russian citizen, and there's no argument that she would left stateless.
https://commonslibrary.parliament.uk/research-briefings/sn06820/ It has always been the case in the UK. I support the law, though it should be used in extremely rare circumstances. In this instance, I think Drobiazko is guilty of a bit more than lack of "political correctness." She is earning her living in an ice show that's run by someone sanctioned by the EU (and the US), and she is married to someone who has had a key role in the illegal invasion of Ukraine. In my view, she's openly associating with and taking money from a war criminal family. That's grounds enough for me.
For citizens of one country, yes. For dual citizens, I'm not sure. Using my own case, the UK has extremely limited extraterritorial rights over me if I am in the US or even the EU.
Agree with the first half; don't agree with the second half. It was clearly disclosed to me at the time I applied for British citizenship that my passport and/or citizenship could be revoked for serious reasons.
How can Lithuania enforce the fine? Lithuania has ZERO recourse against her while she is in Russia. And the US is practically the only country that requires nonresident citizens to file tax returns, so Lithuania isn't seeing a penny from her and never will. Again, they have no extraterritorial rights. Stripping her of her citizenship is pretty much the only thing they can do.