What would prevent a government to pay delegates to retrieve funds identified as tax evaders' possession?
Their is always the option to hard-fork if delegates are corrupted in such a manner. Delegates can be voted out as well. Also, the amount in question must be above a certain threshold before it can even be considered. Ie: a government couldn't bribe delegates to go after the little guys.
Right now we are between people who understands that government are evil, but that's situation is temporary.
Let's suppose Bitshare is mass adopted, a delegate who comply with a western government query will not be perceived by the majority as corrupt, not more than a corporation is perceived as corrupt when it abides by the law of its country.
Historically people are voting to make taxes higher, there is no reason to assume that in a world where BitshareX is mass adopted their opinion regarding taxation will change.
If you implement this kind of tool within the system, people and government will use it.
PS: the treshold is not a security either, let's say it is 10%, if I am a politician who want to redistribute wealth, I can propose to take 10% of the XTS from the richer to give to the poorer.