(For the record, yes--the topic does offend me. However, your work is your work). "In the light of X" or "in light of X" means "knowing X" or "considering X." X is knowledge that helps us see something. A: "Which road should be take, I-84 or I-95?" B: "I-95 is shorter, let's take that." A: "Oh, wait--according to this traffic report, there is going to be major construction and lane closures on I-95." B: "Oh, in light of that maybe we'd better take I-84." "That much" means some amount--vague or precise--that was mentioned earlier, or understood from context. "Do you think a new dishwasher would cost more than $1,200?" "I don't think it would cost that much." "Does not matter that much" means "is less important than X," where X was mentioned earlier, or understood from context. "She thinks that her whole life will be ruined if she does not get accepted by an Ivy League college. I keep trying to tell her that it does not matter that much. Certainly it would be a disappointment, but it would not ruin her whole life." Here, the standard of importance is "a goal so important that you spend your whole life pursuing it." It only seems that important because you are not using good judgement. In the light of better judgement you see something different. What you see is that the goals you were pursuing actually do not matter that much. They do not matter so much that it is worth devoting your whole life to pursuing them.

It's saying that it is easy for males to spend a lifetime pursuing certain goals that don't matter very much (aren't very important). As for 'In the light of better judgement': Light is often used as a metaphor for understanding/realisation/clarity of mind. So it's suggesting that, with better judgement, they wouldn't spend their lives pursuing these goals. Hope that makes sense.