Often the centralized solution comes with a whole bunch of weaknesses.
In the PKI case you'll have to trust over 300 Certificate Authorities every time you make an https:// connection,
many of which are located in countries with repressive governments.
If any of those 300 entities get compromised or malevolent attackers will be able to read your email,
access your bank account, and violate your privacy.
I've been hard-pressed to find any decentralization schemes that would not benefit from Bitcoin integration