History.com is a pretty bad source for Gallipoli. The campaign came up here a few times recently, due most likely to the centenary. Here's a good thread that /u/elos_ , I and some others contributed to:

http://www.reddit.com/r/AskHistorians/comments/33e2gn/everything_i_have_read_has_said_that_the/

To quote /u/elos_:

The application of Gallipoli was what was problematic but the motivation behind it was centered in very real thinking; if anything the British Generals Staff should be praised for their flexibility. Honestly, if I can just get a momentary rant in, this confounds me to no end. Pop culture likes to paint "the Generals", notably the British, as being incompetent swines who couldnt think of anything other than to send men into the grinder; yet in the major example of them attempting something completely different, a seaborne invasion of the Ottoman Empire, they are bashed endlessly for trying something new. It's unfair to them.

Anyways, back on track, yes the motivations behind Gallipoli were sound. The Western Front, in 1915, was a stalemate and it would only be in 1916 that things would pick up again with Verdun/the Somme in the West and Brusilov on the East. The British were very astute in noticing this fact. They did not have a massive conscript army yet (that would be late 1916/early 1917) and their volunteer army was still very, very untrained. The lines in France were not moving very much and, again, they did not have a very large army. However what they did have was the largest and most powerful navy in the world. Where do they use this then? Germany or the Mediterranean. They can't do Germany because the entire principal was to not engage the German fleet; they did not want to give the Germans a chance. It was almost like a mexican standoff between their two navies and the Generals Staff, Churchill in particular, felt it was too risky. So the Mediterranean would be chosen and they would do it against, you guessed it, the Ottomans. The Ottomans with a skeleton force of a navy and an army which was nothing really to speak about; the "sick man of Europe" was prime pickings.

It's pretty easy with hindsight to say that Gallipoli was a bad idea, but it was a fresh approach to the problem of a second front that could have reduced some attritional casualties in Europe. To quote myself from that link:

The Straits were known to be mined, and also to be defended by heavy guns. In the brutal logic of the war, Churchill figured that even losing several older battleships, with their crews, was less bloody in the long term than infantry attacks on the Western front. The problem with the naval expedition was that the Ottomans had a surprisingly stout interlocking defense, both of lines of mines and also of large guns. There's also a pretty significant current in the Strait. So an initial effort by battleships to force their way through was marked by an early defeat (and a bit of timidity on the British part when they discovered the mines). The minesweepers (converted fishing trawlers) the British then bought to the Straits were deeper in draft than the anchored mines, which tended to depress morale among the crews of the sweepers. Nevertheless, they successfully swept at least two of the lines of mines before fire from shore batteries knocked out several of the minesweepers. At that point, they rethought their approach and brought in the HMS Queen Elizabeth to try to knock out the shore batteries by firing over the peninsula (from the Aegean side). This was actually fairly successful, and the Turkish batteries were running low on shot and becoming desperate before the battle of March 18, in which an undetected minefield sank three of the Franco-British battleships and forced a withdrawal. (It's arguable that had the fleets pressed on, the Ottomans might have withdrawn from the peninsula; we will never know. Ottoman morale was wavering and the batteries were nearly silenced; the fleet's withdrawal allowed them to restock and replenish.)

In any case, the failure of the ships themselves to be able to knock out the guns led to a call for a landing at the Dardanelles, using troops to secure the batteries. At that point the Strait could be swept of mines at the fleet's leisure. Unfortunately, that led to Anzac Cove and the bloody fight to follow, where far more lives were lost than those on three obsolete battleships.