Citizen science is increasingly being recognized as an important approach for gathering data, addressing community needs, and creating fruitful engagement between citizens and professional scientists. Nevertheless, the implementation of citizen science projects can be hampered by a variety of barriers. Some of these are practical (e.g., lack of funding or lack of training for both professional scientists and volunteers), but others are theoretical barriers having to do with concerns about whether citizen science lives up to standards of good scientific practice. These concerns about the overall quality of citizen science are ethically significant, because it is ethically problematic to waste resources on low-quality research, and it is also problematic to denigrate or dismiss research that is of high quality. Scholarship from the philosophy of science is well-placed to address these theoretical barriers, insofar as it is fundamentally concerned about the nature of good scientific inquiry. This paper examines three important concerns: (1) the worry that citizen science is not appropriately hypothesis-driven; (2) the worry that citizen science does not generate sufficiently high-quality data or use sufficiently rigorous methods; and (3) the worry that citizen science is tainted by advocacy and is therefore not sufficiently disinterested. We show that even though some of these concerns may be relevant to specific instances of citizen science, none of these three concerns provides a compelling reason to challenge the overall quality of citizen science in principle.