How was Benvolio not impulsive?

Benvolio was always cautious. Consider Benvolio's comment to Mercutio on a hot day that foreshadows a brawl with the Capulets,

I pray thee, good Mercutio, let’s retire.
The day is hot; the Capulets, abroad;
And if we meet we shall not ’scape a brawl,
For now, these hot days, is the mad blood stirring. sact 3 sc 1