What we're looking for here is something that strongly argues against the passage.
E isn't quite that fit. E discusses what happens when professional and DIY projects cost the same. However, the passage is concerned with situations where DIY projects cost less than professional ones, which is usually where people would do DIY projects (to save money.) If they cost the same and people would then generally do professional, it may be true that this removes some of the need for the how-to article. However, people are still going to choose DIY when it costs less, so this doesn't remove the problem.
C is a better fit. C tells us that if people have a DIY how-to guide, they're more likely to do it themselves. We don't want that! The speaker was trying to reduce risk for the people already determined to do DIY, not to encourage more people to take on that risk. If providing a how-to guide would increase the risk, then it does the opposite of what the speaker wants (to reduce risk.) Therefore, C is the best argument against the passage.
