Why should there be evidence ? They have a right to be pro-active and protect themselves from the C-suite.
If you're a junior, or someone trying to get into the field. I can't tell you the right path. But I can tell you, the people with the purse strings care only about that purse, and parting with as little of it's contents as possible, and getting as much out of you in the process of doing it. I can tell you I made the decision over 10 years ago to go the non-organized route. It worked. For a while. But at great personal cost medically, and likewise when I inevitably had to make the choice between becoming the better cog for the market, or being there for the people who matter most to me.
Don't delude yourselves. Organize. The people hiring you do. You must as well. Organize enough, and we as a society may finally recalibrate enough to achieve a new equilibrium that doesn't involve mulching each other for the sake of Mammon and Moloch.