How did secretary of state seward justify his purchase of alaska from russia? why was he criticized for this?

Alaskan purchase was the deal with which USA acquired Alaska from the USA, then secretary of state William H Seward played a key role in the purchase. It Was transferred from Russian Empire to the USA  on 18th October 1867. The treaty was ratified by the Senate and signed by President Andrew Jackson. Although Russia had acquired the land Russians never settled. The Czar was also afraid that due to the Crimean war it won't be easy to hold on to Alaska, and he wanted to sell it. Russians had approached President James Buchanan for the sale but due to civil war, the negotiations could not succeed. After the civil war negotiations Again Started and the treaty was ratified by Senate with a margin of just one vote on 9th April 1867.

Although the treaty added more than 500,000 square miles of area to the US, Seward was Criticized for the purchase because the land was thought to be useless. It was called it Seward's folly, Seward's Icebox, and Andrew Jackson's polar garden. Others were positive about the purchase as they argued that Alaska would help to expand American trade in Asia