he believes the virtual currency should be returned to him because Bitcoins are "not subject to seizure" by federal law.
See the bolded part?
Both you and Ulbricht don't get it. What you believe has no bearing on reality.
Ulbricht isn't claiming that the government violated the constitution. He is claiming Bitcoins aren't property and thus can't be seized under federal law. That is for a judge to decide, but lawyers don't think he will prevail because intangible property is still property and federal law allows for the seizure property that are the products, or purchased with the products, of federal criminal acts.
Unless you were at Waco, you don't know what happened at Waco.
The Tao is like a glob pattern: used but never used up. It is like the extern void: filled with infinite possibilities.