It's an artifact of the technology they use. US launchers are hot launch: the motor ignites in the cell, and then leaps out under its own power. This has some disadvantages with having hot exhaust inside the ship.
Soviet launchers used a cold launcher. They pushed the missile out first, then ignited the motor after it was out of the cell. This is good for reducing exhaust impingement. But you can end up with a live missile not actually going up if the motor igniter fails. Angling the launcher ensures your live missile lands in the water, instead of on deck.
I've seen video of this, but having no luck searching for it.
Fun fact, due to the same design choices US-designed missiles are vulnerable to a failure mode called a "hang fire" (see for example https://www.navaltoday.com/2018/06/25/sm-2-missile-fails-to-... ) where the rocket engine has ignited but the missile is stuck inside the ship for some reason.
The VLS designers had to massively overengineer the bottom part of the VLS "plenum" (the bottom part) to be able to withstand the largest missile that will fit inside a VLS to fully burn out inside it without melting through the bottom and endangering the structural integrity of the ship it is in.
Firstly its a misconception that that VLS has anything to do with this. VLS has only really been mounted on ships from the 80s onwards. The first US ship with VLS was the Ticonderoga class cruiser launched first in 1980, however the VLS was only used for anti aircraft missiles and the Harpoon anti ship missiles were positioned in quad launchers at the rear of the ship. The Soviets did in fact deploy VLS earlier than NATO on the Azov class cruiser, but kept external anti ship / submarine missiles on many designs. Indeed throughout NATO it was common to mount anti ship weapons externally just as the Soviets did right up until the mid 80s. If you think about it, anti ship missiles want to go sideways rather than upwards so it makes sense to point them at where the enemy will be.
Given that the majority of anti ship missiles were external on both sides I suspect the difference in prominence and perception comes from two linked points.
1: The majority of NATO ships were not designed as surface combatants, rather as escorts for carriers
2: Soviet anti ship missiles tended to be bigger with higher speeds and larger warheads.
On the first point the main priority of the US navy is power projection. As such it is generally reliant on carriers to provide strike capability through sorties. This is suplemented by submarines for anti shipping capbilities. THe majority of NATO surface combatants are geared towards allowing those carriers to be deployed unimpeded, as such they have a lot of anti air and anti missile capbility which by nature fires upwards.
The Soviet navy was more focused on area denial as they did not develop a significant carrier force. As strike capbility was not provided by naval aircraft (at least to the same extent) a greater emphasis was put on sinking enemny combatants. As such their ships were designed for surface to surface roles to contest the baltic and black sea. This required them to be able to sink NATO carrier groups themselves which in turn required more powerful missiles with higher speeds and bigger warheads. These therefore which appear far more prominently on their ships. I'd also note that the Soviets tended to put large missiles on smaller ships such as corvettes which made them appear even more prominent.
Russian missile systems were during the cold war (and perhaps still are) superior in many ways to NATO counterparts. The USSR had no problem devloping reliable rocket motors and had some pretty fearsome weapons. I think the idea that they put their missiles on the side to prevent self damage is a little far fetched.
Completely agree with all of this. When you're looking at firing missiles like the P270 and P-700 AShMs that have a mass close to a small fighter aircraft, there's nothing to be gained by vertical launch here.
The USSR and Russia were late getting into vertical launch from surface ships. When they did, it was with larger missiles than the US used, but fewer of them. There were some interesting designs, such as a missile that carried a torpedo, a ramjet-powered missile, and a missile which operated in a group of other missiles with one of them in charge. The USSR built some giant nuclear-powered battlecruisers to carry all those large weapons, and put large vertical launch tubes on some aircraft carriers.
Now, like everybody else, Russia mostly uses vertical launch in new systems.
That said, I think it's more propaganda than a rule. Especially since plenty of Russian vessels utilize vertical launch systems. I believe the necessity of the angled launch systems like what you'd find on the Kirov, Slava, and Kara classes were more due to the immense size of those missiles. Look at the U.S. Talos and UK "Sea Slug" missiles for western examples. As missile technology became better and more miniaturized, you start seeing more vertical launch systems where it makes sense.
The one area I've seen consistent arguments for horizontal launch are in places where a missile failure (see above) would be much more dangerous, such as on a carrier deck. This is why I believe you still see Sea Sparrow and SeaRAM systems placed on the wings and below the deckline, so that a failed launch won't land back on a deck full of fuel and ordinance. The ranges that point defense systems are working at can't allow for a missile body to "tip over" and still hit the target at range.
I'm under the impression the Kirov-class battlecruisers have vertical launch tubes. On the other hand, the concern seems somewhat warranted:
https://youtube.com/watch?v=V88sUJKgOsk
This sounds like some ridiculous cold war propaganda, source?