What is the purpose of Shelley's irony when Walton recognizes he has found the friend he is looking for only to watch him to die? (Letters 1-4)

It is ironical that all of Walton's ambitions have been fruitless. The friend he meets is very like him..... proud, ambitious, and arrogant. Unwilling to admit mistakes or take responsibility. It seems that Walton sympathizes with Frankenstein who considers himself blamesless to the end.