Any essay which focuses on something external at the expense of “this is about me” is a risk. I don’t think the activism is what’s problematic here- the risk is that 95% of the essay becomes about the issue, why the need to protest, etc. and only 5% is about the student.
If it can be done to use the activism as a metaphor for what makes a kid tick than I think it’s fine. But I think it will take a very talented writer to keep the focus away from the topical stuff and keep it on the applicant.