Duh.
My complaint is not that it adjusts speeds. My complaint is that it adjusts speed inappropriately. If I'm going to have fiddle with and drive the car anyway, that defeats the purpose of FSD, and instead of reacting angrily when the car does something wrong that I don't want it to, I'd rather it just follow my command until I tell it to change. This is my complaint with FSD. Yes, following speed limit signs is great, but there's more to driving that just following a black and white rule. That's why I'm waiting for the quality of FSD to improve before I pay $15,000 for it.
I totally get where you're coming from, but I think you'll be disappointed. I don't think the system will ever allow the driver to just set a speed and the system stays there until you change it (like the old cruise control).
Here is what I've found:
1) Enable AP, and the speed will be whatever the speed limit is, or if you're driving over the speed limit, your current speed.
2) Adjust the speed to whatever you'd like it to be using the wheel
3) The next speed limit sign it finds, it will likely adjust the speed to that speed limit. Adjust the wheel again to what speed limit you'd like
4) The car will maintain that speed, even if it finds a new speed limit sign (with a catch)
There is one catch - there appears to be some set timeframe in the code, where the car will maintain your set speed as long as you stay on the same road, and it keeps seeing speed limit signs with regularity. If it doesn't see a speed limit sign for some period of time, then it will adjust the limit the next time it sees a sign. In SoCal, speed limit signs on some of the freeways are sparce for some reason. There are a few stretches were there are no speed limit signs for 15-20 miles, so when the car finds its next one, it may adjust speed back to that sign's limit.
Another caveat is construction zones. Be very aware when in construction zones, especially ones that create a new traffic pattern by shifting lanes. Tesla does not operate on visual alone and does take map data into account. If you watch carefully on your map, you may find that the car suddenly appears off the freeway/highway when the lanes shift for construction. The car thinks, via GPS, that it's now on a side street instead of the freeway, and that side street has a speed limit of 45MPH, so the car will suddenly begin braking. When you feel that braking, check the speed limit displayed, and you may find it's showing 45MPH instead of 65MPH or whatever the limit on your freeway. Whenever I see the lanes shifting due to construction, I either disengage AP through it, or watch the speed limit like a hawk and prepare to wheel up in the event the car adjusts the speed.
If this all sounds too much for you, as I said previously, you will likely be disappointed. ADAS and AV laws are very new, and regulators are slow to catch up to the dizzying pace that technology is moving. I think it's very likely that regulators will ultimately publish requirements that cars with advanced hands-off ADAS (L2+ and L3) will be required to travel at the posted speed limit. It may be why Tesla's can be overridden by the driver, but eventually lock back to the posted speed limit, especially if they're changing roads (one freeway to another or entering/exiting the freeway).