That's the benefit we can enjoy in the decentralized system. As long as you hold your private keys safer no one can seize your bitcoins. But when we go for online third party bitcoin storage like wallets, and we do not have private keys there are chances to be seized by the third party.
As of now, we can assure it. But it seems the some local governments are showing their interest to bitcoin. They may not control bitcoin as it is decentralized but for sure if they announces complete adoption of bitcoin they can do something in their favor. Just like putting some value added tax for each transaction that we will do with our local exchange sites.