We shall just have to agree to disagree, then. From my point of view, it is polite to ask permission if you are going to interfere with the comfort of another person, whether that is by raising or lowering the blind, or indeed in any other way. But I appreciate that you have a different view.
"interfering" would be
lowering the blind; the status quo / default position is that the blind is raised.
The default expectation of any passenger would be that they would be able to see out of the window and if anyone wants that to not be the case, the onus is on them to check that the other passengers are okay with it.
There is perhaps a debate about if someone else sits nearby who would be affected by the blind being lowered but I don't see it as a valid argument that you should be able to change their expected environment without saying anything to them to check they are okay with it, but they should be checking with you to simply restore the status quo, and that it's acceptable for you to say nothing but not acceptable for them to say nothing, but I accept that's a nuanced and subjective point which may vary depending on the specific circumstances.
But, for sure, those who want the blind lowered need to be mindful that this is not the default position and they have no entitlement to it, and that it should only be lowered if all those affected by it are happy for it to be in the lowered position. This is especially the case on Pendolinos, as described earlier on the thread, where it's not just about having a view or knowing where you are, but many people would feel ill if they cannot see out.
You don't have to seek someone's permission to not feel ill, when the default position is that you wouldn't feel ill!