Fascism is not "a form of capitalism" it is another form of socialism. The difference is that that under communism the means of production are outright owned by the state where as under fascism the preserve the illusion of individual, i.e. capitalism style, ownership. Actual economic control economic control under Fascism is actually state controlled. So it is not accurate to claim that Fascism is a form of capitalism it is more accurate to say it is a variation of Socialism. Just as Communism and the post war European economies are all variations of Socialism.
As whether Communism requires tyranny it would seem that in practice it does. Simply because there are no examples where both Communism and freedom have co-existed for any significant period of time. From the evidence of what has happened it would appear that the level of control required by Communism, and Fascism for that matter, is simply unachievable without coercion. Entire populations simply don’t like surrendering complete control over their lives to the government. So no matter how high minded the Communist authorities start out they invariably have to adopt tyrannical policies in order to enact their program. Simply because there are always too many people who do not want it to enact it any other way.
Where Socialism has managed to exist without becoming a tyranny is in places like Europe. Where they adopt a limited amount of Socialism but still allow people to pretty much live as they like. Socialism without freedom and a certain amount of Capitalism ends up in tyranny. Capitalism without a certain amount regulation and government intervention, i.e. Socialism, ends up in a different kind of tyranny. Fascism and Communism are just variations on the same theme and both invariably lead to tyranny.