When I click on the sources tab in Family Search and find a source connected to a profile I cite the source in the Family Search database, not the profile.
Even those citations need to be evaluated. I have lost count of the number of sources attached incorrectly on fs. It's not just the multitudes of duplicates that get wrongly merged, thus creating massively conflated profiles; it is the number of sources attached because the name is the same, without any thought as to whether it is the correct person being referenced.
I recently worked on a line where there were same-name cousins, a decade apart. The sources for one were attached on fs to the other. I have detached sources for a person who lived in the mid1800s to early 1900s, because the person to whom they were attached lived in the 1600s. I have detached spouses / children for the same reason.
This is why ALL sources need to be evaluated as per WT guidelines : "Our requirement for modern profiles is only that you say where your information comes from. We do not attempt to enforce any standard of reliability for sources or any method for securing pre-approval except on pre-1700 profiles.
This does not mean that WikiTree members do not need to evaluate the reliability of sources. Evaluating sources and the evidence they contain is part of the science of genealogy. As genealogists, we all need to do it. And as collaborative genealogists, we need to tell each other our sources so that we can work together to evaluate their relative reliability. For help evaluating the reliability of sources, see Help:Uncertain or ask in G2G."
(Bolding is mine.)
A source, according to WT, is where you find the information. Ensuring it is reliable comes after that- and often only after education, and / or assistance.
(It's why project "Trails" are a good thing. They help to educate.)