Scientists Can't be Advocates!: In My Humble Opinion...
I don't think scientists can also be advocates because it could make them biased or corrupt. If they are advocates for a cause and decide to do their own research, their results could be biased from the beginning. I say this because they might be looking more carefully for the results that they want to see or even tweak their data to fit their desired results more closely.
Another issue is that scientists being advocates could also make them corrupt. There have been so many cases where big companies (like the oil industry) that pay scientists to discredit other scientists work or tamper with their own work to please the company. Some argue that scientists are less likely to do this because it will ruin their name in their field, however, people do a lot of things for money so you still never know.