I'll play! Define "unreasonable".
I can think of two definitions of unreasonable.
The first is subjective. It's definition relies totally on opinion of the person making the assertion. "I don't think $5 for bananas is unreasonable". You could easily substitute 'normal' for 'unreasonable' in these sentences and not change the meaning of what was said.
The second definition is objective: That which occurs without reason. As in, "If you want to search someone, you need a reason to suspect them of a crime." You could substitute 'personalized suspicion' for reasonable in that sentence without changing the meaning of what was said.
The subjective definition has no meaning but what one chooses to assign to it, based on one's own opinion. Unfortunately, this is the definition courts have chosen to use. Because 'unreasonable' means anything they want it to mean, it becomes meaningless. Such a definition used in context of the 4th Amendment is akin to having no 4th Amendment at all, because government ultimately will have the final say on what is 'reasonable'. Since their pronouncements of what constitutes reasonable behavior changes over time with the fickle whims of the courts, it is by definition a 'living Constitution' interpretation. The court has used the 'reasonable person' test as a measure here. That is, if they believe a 'reasobable person' believes they have a right to be free of search, they may uphold their 4th Amendment right. But note, that as 4th Amendment protections diminish over time, what a reasonable person may expect will diminsh as well. This can lead to nothing but an ineffective 4th Amendment, which is precisely what we have now, and quite on purpose.
It is my strong belief that the founders intended the use of the objective definition. As rights are inherent and unalienable, they do not change over time or with people's perceptions or opinions. The objective definition stands the test of time and is beholden to no one's whims. Also, the 4th Amendment was the Founder's answer to the King's General Warrants, which were used to search people who lacked any individualized suspicion, in other words, fishing expeditions.