Censorship?

1967 is the year the censorship in US was diminished. However, there has existed extremely violent films earlier than that (Blood Feast for instance) and at least in other countries, films that have been relatively explicit. If we take Onibaba for instance (also Japanese), there's a scene of a (nude) woman rubbing herself against a tree to gain sexual pleasure, this is something that would probably been unacceptable in USA at the time of the film's release (1964).

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Japanese censors (aka "ratings" boards) have always been far less stringent with sexual and violent content than their American and British peers. By the late 1950's, "pink" films (pinku eiga) were being made which showed graphic depictions of sexual content (but no actual sexual contact- which is still illegal in Japan). Violence has always been a far more exceptable taboo in Japanese cinema (and artistic culture in general). The jitsuroku eigas ("real life" yakuza) films which appeared in the 1960's and 70's were extremely violent and graphic (especially with camera work such as *beep* and Suzuki's films). In fact, one of the few films to actually be re-edited due to violence was the *beep* infamous Battle Royal (which was prompted more by the age of the actors engaged in the violence than the violence itself).

The Japanese rating system for theaters has always had an "adults only" rating that doens't carry the stigma of the American "X" or "NC-17". The adult rating in Japan ,I believe, doesn't necssarily mean there's going to be lots of sex, but that there will be scenes and situations that only adults would understand.
Suzuki himself said his picture assignments were intended for this adult rating.