He is called Mahatma because people called him so. Those people and their children are dead along with him so it is easy to dig-up dirt on him. I read a great quote somewhere - 'nobody becomes a leader without doing questionable things'. I firmly believe it to be true for Gandhi and MLK and Jesus, but that doesn't steal away the fact that he was indeed a great leader of Indians and the whole world looked up to him for non-violence.
Regarding him being a wife-beater, I want to know your sources. I know for a fact that RSS propagates a lot of lies about Gandhi and Nehru family. I firmly believe he practiced non-violence and was NOT a wife-beater, WAS against caste-system, WAS against British rule over India. His secrets that are coming to light now (such as his sexual deviations) are things that were public when he was alive but almost nobody cared, or cared enough to propagate. Today, his legacy is major political problem for India and so it is being dug-up by some, while others want to hide it.
Whether he was responsible of India's independence or not, I don't know if it can be debated after 70 years of the fact. And I don't think one will ever get to the 'facts' by debating on this point. The maximum one can do is to read more and form informed opinions.
On-topic, while I agree that 'you can dig up endless dirt on the successful', the topic here is not the dirt, it is the person himself. Gandhi didn't become Mahatma because he was a 'racist' or 'wife-beater' etc. But Steve Job became successful due in large part to him being an asshole.