My recommendation is:
It will be said that men will not work well if the fear of dismissal does not spur them on. This is true of only a small percentage of men at present.
I have removed "I think" because it weakens the sentence. You are, by definition, discussing your thoughts.
Although you didn't ask for comments on the first sentence, it is also awkward, despite being technically correct. You could greatly simplify it and make it gender-neutral by rewriting the whole thing as:
It has long been said that the fear of losing their paycheck is what makes people work, but most workers these days are motivated by deeper goals.
This may be an acceptable solution for you if your essay is going to be about people's reasons for working. If that is not the case, I suggest you play around with the words in your original sentence until it sounds more natural.