I heavily depends on what your non-profit does (help people with cancer?) and on what porn sites you advertise, but in generall I think it is a bad idea.

For many people porn and fast food are BOTH "guilty pleasures" so food adds are a great idea, beacuse the audience is already in the right mindset.

People visit porn sites to get some exitment and relief, or to get into the right mood (Fk the rules / I need something to cheer me up/ Lets stay in bed).

Your add will remind the visitors of something they SHOULD care / worry about and will ruin the experience.