I feel it worth pointing out that in 1903 (when Britain and Russia were still definitely rivals) a conference on imperial strategy had concluded that the Straits were not vital to British security - which, when you think about it, makes sense. We controlled Gib and Suez (and the seas around Malta) and could easily deploy a fleet in the Med or prevent any rival fleet from leaving it. Bearing all this in mind...
Either the Russians can outmatch the Ottomans in the Black Sea, or they can't. If they can't, there isn't any problem (except maybe that the Germans are getting control of things, but that's another matter). If they can, they can overwhelm the Ottomans and capture the straits - unless of course Britain deploys the fleet to the Black Sea. And what exactly is better about fighting the Russians there than in the Eastern Med, on our terms and nearer our bases? It's not like there's anything we urgently need to defend in the Aegean.
At the time, the patriotic legend surrounding the Straits (originating in the 1850s yellow-press under completely different circumstances, but long since ballooned out of control) meant that no British government could come out and say this, but it was the opinion of the navy brass. By 1914, we'd left the whole Med in the care of the French navy, having a certain problem of our own at Kiel (which, though the Jingo Atlas doesn't make it clear, is closer to the island than Constantinople

). Our attitude to Russians ambitions towards the City during WW1 probably
was "You want it, you go and get it". As RGB says, the getting it is the difficulty; but people are really exaggerating how much Britain (and France) would care.
Alsace it was not, but the idea that the western Entente would suddenly and decisively turn against Russia over a Russian Constantinople during a *WW1 conflict is basically unfounded. And as for France, the French bankers had a big interest in Ottoman state debt which kept them broadly pro-Ottoman (indeed, pro-German) throughout the early 20th C - but Poincare was for the industrialists whose investments were in the railways of the Ukraine, and anyway there wasn't much the bankers could do about the Ottomans declaring war on France. So discount that factor, and why is Russian control of the Straits worse for France than German control of same?
A lot of the stuff being said here strikes me as received wisdom.
After Kemal rupublicified (is that a word?) Turkey in 1923, would it have a reason to hate Communist despots?
Or was it less freedom loving than I think?
Kemal and Lenin were just about one-another's only allies in the postwar chaos, and Turkey stayed on pretty good terms with the USSR throughout the 1920s.