I do not think it is as black and white as you describe it. The way I see it: if somebody falsifies a complete repository, the only way to detect that it was changed is by comparing its content or a hash thereof with that of a (supposed) copy that is more trusted.
That is true for any digital archive, including those made by any SCM system. The only thing where git differs from svn in that respect are a) that it computes such hashes for you, and (typically/AFAIK) shows those hashes in its UI, and b) that it is typical for people to store those hashes on other systems. The net effect of that may be large or small, depending on the number of people keeping a copy who will not blindly copy changes from the 'main' repository.
>I do not think it is as black and white as you describe it. The way I see it: if somebody falsifies a complete repository
No, it is. You can't "falsify a complete repository". We will all have checked out from that repo and as soon as someone replaces it with a fake none of the hashes will match up.
>the only way to detect that it was changed is by comparing its content or a hash thereof with that of a (supposed) copy that is more trusted.
Which happens in the system automatically. Have you actually worked with Git? Go change history on something you've pushed and other people have pulled.
>number of people keeping a copy who will not blindly copy changes from the 'main' repository.
It's not about "blindly copy changes". If you pull from a repo where someone has tried to rewrite history you'll see duplicate entries all over your log. If you have a graphical tool you'll see right where they started their modification.
That is true for any digital archive, including those made by any SCM system. The only thing where git differs from svn in that respect are a) that it computes such hashes for you, and (typically/AFAIK) shows those hashes in its UI, and b) that it is typical for people to store those hashes on other systems. The net effect of that may be large or small, depending on the number of people keeping a copy who will not blindly copy changes from the 'main' repository.