Interest groups are often criticized for being "single issue." This means they will support whichever political candidate promises to champion their one issue. The political candidate could have a terrible platform regarding every other issue, but as long as he or she supports the issue the interest group is promoting, the candidate will get the group's money and votes.
To use a non-partisan example, a powerful, well-funded interest group might decide they will only support a candidate who agrees to ban green hair dye. The honest candidates might say, well, that is completely ridiculous, and I will not support that, because I stand for creating jobs, cleaning up corruption, etc. The interest group, however, could easily use its money to defeat these sensible candidates. The person who got elected might destroy jobs, be corrupt, and not even believe in democracy, but he or she would get elected because of supporting the hair dye ban. He might even do grave damage to the economic interests of the people who voted him into office.
Many therefore say that groups should support candidates not on the basis of single issues but based on a broad range of issues that might work together to make the world a better place.