In "The Crucible" is John Proctor a hero or do you see him as foolish when he might easily have saved his life?

This depends on your own personal opinion, but let's look
at some different angles from the play itself.  At the end of the play, Reverend Hale is
going to all of the prisoners and telling them that not confessing is committing the sin
of pride, at the cost of their own lives.  And, this can be seen in John.  He tells his
wife at the end that one reason he hasn't confessed is because "it's hard to give a lie
to dogs."  He admits that he doesn't want to give his accusers something that they want,
because he doesn't like them.  So, that is pride, or foolishness on his
part.

On the other hand, he is a hero in the sense that he
doesn't lie, and refuses to defame his friends when he almost confesses.  They want him
to name others when he signs his confession, and he refuses; that is the right choice. 
Also, they want to post his confession on the church door; he knows that this will ruin
his children's lives--they will forever be known as the sons of a witch who sold out his
friends.  And, when he finally rescinds his confession and goes to the gallows, he feels
good about himself for the first time in forever.  He says, "I do think I see some shred
of goodness in John Proctor."  He feels that one act of integrity wiped out previous
sins.

So, it can be argued either way, and  I hope that
those thoughts helped a bit; good luck!