That's a good question, and a tricky one to answer.
Criminal law is based on the concept of crime and punishment. Depending on the crime, the punishments can be very severe (e.g. loss of liberty or life).
Permitting ex post facto criminal laws would allow legislatures to arbitrarily criminalize actions that were perfectly legal at the time they were committed.
Given the potential severity of criminal punishments, this just lends itself to abuses of power. Because of this, most countries explicitly disallow retroactive criminal legislation in their constitutions.
Civil law pertains to rights and duties. In this context, there are legitimate occasions where retroactivity may be useful.
Sure, retroactive civil laws can still be used to target specific entities or persons. However, the potential negative outcomes are milder (at most, the loss of movable or immovable assets).
Because of this, there is no universal consensus on retroactive civil laws. Most countries allow them; many other countries frown on them; a few ban them outright.
Criminal law is based on the concept of crime and punishment. Depending on the crime, the punishments can be very severe (e.g. loss of liberty or life).
Permitting ex post facto criminal laws would allow legislatures to arbitrarily criminalize actions that were perfectly legal at the time they were committed.
Given the potential severity of criminal punishments, this just lends itself to abuses of power. Because of this, most countries explicitly disallow retroactive criminal legislation in their constitutions.
Civil law pertains to rights and duties. In this context, there are legitimate occasions where retroactivity may be useful.
Sure, retroactive civil laws can still be used to target specific entities or persons. However, the potential negative outcomes are milder (at most, the loss of movable or immovable assets).
Because of this, there is no universal consensus on retroactive civil laws. Most countries allow them; many other countries frown on them; a few ban them outright.