From a historical perspective I would agree with Kant. Throughout the years, society has tried to calm the masses through fear rather than education. This is more noticeably during the dark ages and prior, when there was a need to find an explanation to things that human beings could not understand. Hence, the importance of coming up with an invisible answer has always been the solution for many different groups at different stages of history, and even during pre-history, where we see that even our ancestral primitives would seek answers in signs from nature to bring closure to situations such as death, loss, and the lack of basic needs.
Hence, we all create an answer to our questions by creating a system of belief ruled by one specific almighty power to which we can reach out in moments of ignorance and doubt.
This almighty power has been diversified through cultural scenarios and specific times in history. It is a consistent paradigm that such almighty being brings the promise and justice humans so distinctly crave.
In the case of the dark ages, it was through proposing fear (and not education) about such almighty power that it was possible to control the poor, sickly and ignorant masses that could have threatened the status quo.
That same system has continued throughout time, and even today we see people divided, grouped, and self-labeled according to their specific system of belief.
Hence, to answer your question, it is not that God is necessary, but that it "necessarily exists" because throughout time it has come as a symbol of power, control, and instant gratification to the curious mind of individuals. It has also, unfortunately, been the reason behind wars, division, separation, and horrible misunderstandings. Yet, it seems to be a necessity in specific groups of people.