A fellow from Kazakhstan here. Banning this certificate or at least warning the users against using it WILL help a lot. Each authoritarian regime is authoritarian in its own way. Kazakhstan doesn't have a very strong regime, especially since the first president resigned earlier this year. When people protest strongly against something, the government usually backs down. For example, a couple of years ago the governme…
What is the extent of the MITM attack that you can do with this certificate? Can you intercept all https traffic?
On its own the root does not magically intercept the traffic, so Kazakh ISPs will need to do a bunch of (potentially quite expensive) work to actually MITM traffic for the Kazakh government, but with the root once that work is done it doesn't get flagged as a problem.
Because this exact same strategy (root that is not trustworthy is installed) is used in corporate setups to do anti-exfiltration, porn filtering and dozens of other things of dubious value, browsers are designed to let you, or the computer's administrator, choose to trust root CAs and indeed lots of counter-measures that protect ordinary users from bad guys are deliberately _disabled_ in the scenario where you've told it to trust some third party. You know best.
If you imagine a hypothetical system which just doesn't trust this root, say somebody has a Raspberry Pi they smuggled across the border, or more prosaically, they just said "No" and refused to install the root certificate -- such a system just will treat the MITM as an error, your secure web browsing won't work because it can't make a secure connection.
Or contrariwise, suppose you install the root in an otherwise ordinary PC in New York connected to AT&T, it will have no effect because the Kazakh government obviously isn't in New York MITMing your connections to other stuff.