It is a very cheap and effective way to achieve this.
Spying on the population is not prevented by GeoTrust and Cie's loosy certificates, a lot of literature and real life examples already show that. This is a tragedy of the commons, until everybody has access to REAL security, then no country has interest in having foreign powers spying them while not even being to do what everybody else does.
In France, Germany, Italy, Japan, Korea, Australia, etc, all of your data is already analyzed and deciphered, they freaking work together to make it less obvious than Kazakhstan. Don't make any mistake and don't call for overthrowing the regime there, it makes no sense.
From a citizen PoV, they became almost as watched over as we are for WWW traffic, but their lives are still not as much tracked as ours since they do not have the means of our agencies. They are still better off than us.
Even if what you said is true and western countries have private encryption keys of all websites I think that citizens of Kazakhstan would rather be spied by foreign governments than by their own government.
Not "ensure". MITM. It provides no security benefits. But it might provide another attack surface for additional malicious adversaries (criminals and other governments).