The consensus of the "professionals" (Fisher chief among them) was that forcing the Straits by a purely naval action would have resulted in a disaster: IIRC the estimation was that at least 2/3 of the capital ships involved would be sunk, and most ot the others would be seriously damaged.
Please don't mention Churchill: the First Lordship is a civilian position, and should have never have been involved in operational decisions. Obviously Churchill being Churchill bullied every one else and wanted to micromanage issues which he was neither competent nor entitled to meddle in.
There were 4 different but synergic defenses in the Dardanelles:
- the layered minefields were the main defense. They should have been cleared by fast minesweepers, but these were not available for the Dardanelles front, even if the British navy commanders in the Mediterranean had been requesting them since mid January. Instead fishing trawlers manned by civilians were used,and these could not move faster than 2-3 knots given the strong adverse current in the strait current
- the second defense (fixed batteries protecting the mine fields) were quite effective against slow-moving trawlers
- the third defense consisted of quite a large number of mobile howitzers, which were almost impossible to be silenced by ship guns
- finally there were the forts, which could send plunging fire against capital ships. While the forts at the mouth of the Dardanelles were (partially) reduced by ship guns, the same was impossible for the forts further down (it was not possible to observe the hits and direct the fire). Anyway even the outer forts required landing parties to demolish them with explosive charges
Add to this that the Ottomans had ample reserves of ammunition by the end of February, while the British commanders had orders to avoid wastage since their own reserves of shells were limited.
Another problem was represented by the need of supplying the capital ships which might eventually reach the sea of Marmara: it had to be done with unarmored ships and colliers, easy prey for the mobile howitzers, and in any case the minefields would have been replenished again after the capital ships had passed.
What should the few ships which might eventually reach the sea of Marmara do? Shell Constantinople? The same ships sooner or later would have to run again the gauntlet of the Narrows to reach the Aegean sea and safety.
It is quite obvious that any naval action should have been strongly supported by landing a serious number of soldiers on the Gallipoli peninsula, to silence the mobile howitzers and the batteries protecting the minefields, and to observe and direct the naval shelling of the forts. There were about a quarter million Ottoman troops in the area, 2/3 of them on the European side with good communications and prepared positions. How many troops should have been landed by the Entente? From where should these troops be taken? The British command on the western front was deadly against releasing even a single line division, and Kitchener himself was at best lukewarm, and quite relieved when Churchill pushed for a purely naval action.
Forcing the Straits (landing plus naval shelling and mine clearing) might have conceivably succeeded in late 1914, assuming a professional preparation and a surprise element. Doing it in 1915 was an exercise in madness.
Incidentally, the Russians asked for a "demonstrative action" to relieve the pressure; forcing the Straits and knocking the Ottomans out of the war was a horse of a very different color.