No, no, and no.
The 4th protects against “unreasonable search and seizure” by making law enforcement present a warrant to a judge. The judge, supposedly, decides weather the search is reasonable or not and signs the warrant. If he determines it is unreasonable then it doesn’t get signed. Just because it says “unreasonable” searches doesn’t give law enforcement the power to search just because they think the search is reasonable. And, just because law enforcement and the government has been violating the 4th for years doesn’t make it lawful or Constitutional.
Why bother with a warrant in the first place? Why would a warrant even be mentioned? Are you saying that you only need a warrant if the search is in fact unreasonable?
I suggest that you do some reading on the history of the Fourth Amendment, and on searches and seizures generally, before asserting that warrants are required before a search is conducted.
You are correct that just because the officer believes that a search is “reasonable” does not, in and of itself, make it constitutional; the person searched certainly can have an opinion different from that of the officer, and if he is charged with a crime the reasonableness of the search will be determined by the judicial system. Unfortunately, because of liberal judges, only when the cops actually find evidence of a crime in a search does the reasonableness of the search become an issue, and cops are free to harass innocent citizens all day long without any repercussions.
“Why bother with a warrant in the first place?” Because if the officer has a warrant no one can say “Boo” to him, and he is immune from any possible claim. The Framers wanted to limit the ability of officers to obtain warrants, given the abuses that took place when British authorities would issue “general warrants” that allowed cops to search whatever they wanted with no repercussions. That’s why the Fourth Amendment has such strict requirements for being able to obtain a warrant: probable cause, and specificity of the place to be searched and the thing or person to be seized.