Organizations such as Steam (software) often offer sales where certain games are available for low prices--in order to compel or persuade buyers to make donations to worthwhile charities. Cueball is participating in one of these purchases (to fight malaria), but Megan's snide denigration of Cueball's act of charity as inadequate and self-serving has dissuaded him from any act of charity at all, if this is what it gets him. It is not a positive force; instead, her mockery dissuades him from donating again to charity and (because she will not humbly consider the effect of his actions) does not lead to her giving to charity, either.
It is important to note the third panel, in which a totally normal conversation is had where purchases are not evaluated on a global scale. Most people do not say "don't buy that video game--donate to charity instead!" on a regular basis. People do however say, "Why did you buy that game for ten dollars and only give the other ten to charity, instead of all twenty?" Supposedly these kinds of conversations happen to Randall on the internet, so a good way to avoid them would be to avoid starting stupid and meaningless discussions there.
The proper response, of course, is to neither care what people say about you nor attack other people's charitable giving. The action that Randall recommends here is to right one, which is to donate anyway without caring about what others say or do. Clicking on the original image leads to the website of Nothing But Nets, an organization that distributes mosquito bed nets in Africa for the eradication of malaria.
- Cueball: I'm going to buy this $10 game I want, and I'm donating $10 for malaria eradication.
- Megan: If you actually cared, you'd skip the game and donate all $20.
- Megan: What's more important? Games, or mosquito nets and medicine for kids?
- Cueball: I think I'm going to buy these two $10 games I want.
- Friend: Cool; which ones?