I think there are two answers, so lets take the easiest first. Should science be political? No. Science, the act of researching and presenting results should not be political... well except when the experiments involve living beings or could hurt living beings, but that's more about ethics and regulations on types of experiments allowed. But the research, the data collected, the communication of results through publications and conferences should not be silenced or manipulated for a persons or funding agencies own political views.
Now I'm sure it's not quiet so black and white and a bit more grey then I've written here, but lets move on to the scientists. Should scientists be involved in politics? Yes! At the very least, without informed decisions we can't have good policy. The ultimate end goal of science is to understand the world around us and help improve our lives in it. Often this means that science and research is seen as turning into technology or medical advances, but it also leads to policy and regulations.
Take for instance seismology. Understanding how earthquakes propagate, and how large they are likely to be has informed building codes. Or how about my beloved space weather? Well, there's a space weather research and forecasting bill introduced to the senate right now looking at understanding what the effects are on power grids and oil pipelines as well as on aviation and many other aspects of our lives. And of course there is the big one, climate science.... but I don't think we need to go into that here.
Since much of science can inform policy, we need scientist to be involved in politics and to communicate this information. Scientists also need to be involved in politics to make sure that this pipeline stays open. We saw earlier this year how the government felt that it was appropriate and perfectly fine to gag scientists, not allowing them to speak as well as "reviewing" the data and results before they went public. Sure we sometimes have to do this to make sure it's not classified or competition sensitive, but what they were starting was well beyond this, removing already public data.
The government also often makes a lot of policy that effects scientists! For instance here's a list of some of the current legislation that could effect my field:
1) The Space Weather Research and Forecasting act
2) The Inspiring the Next Space Pioneers, Innovators, and Researchers and Explorers (INSPIRE) Women Act
3) To direct NASA to return humans on the moon and to develop a sustained human presence on the moon
4) A manifest for human space flight
And many many more. Some dictating the way lab waste is treated, others discussing what federal regulations contractors have to follow or not follow, and a few more on humans in space or going to the moon or mars. Many if not all have been advised at some point by scientists. And scientists should be commenting on them all! Anyone with an interest in space weather research should read and write/call your representatives about them!
And for the last and most important reason... Which really should be self explanatory... Scientists are citizens and it is our civic duty to be involved in our government.