How is declaring that they are whatever the USSC and/or Congress last said they are any less subjective? Once you have abandoned the test of original intent in favor of contemporary opinion (regardless of who's opinion you choose to subscribe to) you're in Living Document land.
What's the original intent of "unreasonable" to which you referred? And how does this original intent apply to the internet? Or planes? Or automobiles?
"Unreasonable" has to be defined by someone, tacticalogic and be applied to every citizen equally. Who defines it in your fantasy world? I really want to know.
Yes, the Constitution is a Living Document -- it may be changed via the amendment process. Aside from that, it is interpreted by the USSC.