I don't how Google's auto suggest algorithm works exactly but if it shows the most queried results matching the initial keywords without filtering those with negative connotations, its a time to worry, especially for parents & teachers. What impact can it have on teenagers & younger kids?
SafeSearch screens only for sites that contain explicit sexual content leaving other sensitive topics.
Displaying an auto-suggestion like "how to hack gmail password" when a teenager begins typing "how to" is sure to misdirect innocent minds & put ideas into their head. Autocomplete is on by default & disabling this under Preferences is the alternative for those who are concerned.
Thank God, a suggestion like "how to make a bomb" (returns 81,700,000 results in 0.05 seconds, BTW) doesn't feature in the suggestion list...yet.
Also see:
See what Google is suggesting
Look what Google Goggles visual search can do