Users are moderated mostly by each other and ultimately by moderators.
The fact that one user did a lot of protecting of questions is not, by itself, a problem. Many questions need protecting due to attracting too many low-quality answers. As one of the site's most active reviewers currently, TheLethalCarrot probably sees a lot of these low-quality answers, which puts him in a good position to know which questions need protecting. However, all of these actions can be undone if necessary:
- If you see a question which was protected and shouldn't have been, you can unprotect it.
- If that turns into a protect-unprotect war, or if there's a pattern of bad protections, you can raise a moderator flag and ask us to look into it.
The above is pretty much a scale model of how Stack Exchange works overall (although question protection is a very minor and less-important aspect of the SE model, not likely to cause much harm either if underused or if overused).
Stack Exchange is moderated mostly by the users. Thanks to reputation-based privileges, someone who's contributed enough content to the site gains the power to close, reopen, delete, undelete, protect, unprotect, etc. This is on a strictly volunteer basis, so a high-rep user who doesn't want to take part in these activities doesn't have to. The natural consequence is that some users will do more moderation tasks than others, by way of being highly active on the site or simply being more interested in this kind of work.
To some extent, the system assumes high-rep users are trustworthy (there's even a privilege level called Trusted User). To spot mistakes, the system also relies on users monitoring each other: if someone makes a mistake or acts in a wrong way, it's likely that someone else will notice (see the first bullet point above). Wrongly closed questions can be reopened, and so on. There are various pages which enable high-rep users to review each other's actions: the one you linked about question protections, reviewing reviews in each review queue, etc.
If things escalate beyond that stage, or if someone has gone completely rogue, then users who notice the problem can escalate to moderators (see the second bullet point above). Some situations can't be dealt with just by user-on-user discussion. If there's a rollback war in edits or a close-reopen or delete-undelete war, a moderator can lock the post pending a final decision. Some situations, such as a user becoming abusive or refusing to desist from destructive behaviour, require extreme action like suspensions.
What is the actual problem here?
The above is general stuff about how the Stack Exchange model works, which resolves the general "quis custodiet ipsos custodes?" issue. But you seem to have some specific grievance here; you say:
he/she is inflicting a lot a influence that I think is detrimental to this site.
What exactly do you think is detrimental? You haven't raised any actual problem here. You've mentioned a user who protects a lot of questions (but you haven't mentioned any cases of a wrongly protected question), and a user who made a mistake in closing a question (mistaken closures happen a fair bit, and usually don't call for further action beyond reopening that question). Is there a problem that needs to be dealt with?
I understand that you may not want to air detailed concerns publicly. If there's a real problem with a particular user's behaviour, feel free to raise a moderator flag, or ask me to open a private chatroom if you want to say more than fits in a mod flag.