The question as asked demonstrates a lack of comprehension regarding Hinduism. Just like how Christianity has dozens if not hundreds of sects with slightly varying viewpoints, so does Hinduism. While the Hare Krishnas may not be the best representation of Hinduism, like it or not, they are a part of that belief.
I believe the Hare Krishna movement should be considered separate from Hinduism because they are absolutely not the same thing. The International Society for Krishna Consciousness was founded in New York in 1966 and its core beliefs are only based on a few select traditional Indian scriptures, not the entire collection found in Hinduism.
Unlike many faiths with rigid structure, strict doctrine, and centralized authority, Hinduism stands apart as being the most diverse, yet most inclusive, faith in the world. There is no dogma in Hinduism preventing it from easily encompassing many other faiths, including Hare Krishna. Hinduism even includes some other major faiths. For example, many Hindus claim that Jesus is an incarnation of Vishnu, just as are Rama and Krishna. Hinduism has traditionally included as many different types of belief as there are types of believer and there's no reason to change that now and begin exclusion of any other faith.
Whether or not this movement should or should not be considered separate from Hinduism is completely up to the people who are in this movement, and depends on what they believe in. If they believe they are not Hindu, then yes they should not be considered the same as them.
The Hare Krishna movement is an offshoot of Hinduism. Without Hinduism, there isn't Hare Krishna. It's like Islam and Christianity can't exist without Judaism since the initial monotheistic religion involved children of Abraham and Isaac. Hare Krishna, much to the chagrin of some Hindus, is part of their religion whether they like it or not.