Also there are things like music, pictures and documents on there. The catch is that when you have 10 TB of data it's expensive to build an entire extra system for a backup. Drives don't cost that much but you also have to consider a case, motherboard, RAM, CPU and so on.
It is usually a good idea to separate out hard to replace files like pictures and documents, from easy to replace files, like movies and music. That way you can easily do a thorough back up of the hard to replace files (which are probably relatively small in size).
As for people saying that the value of time to replace movies is high compared to the price of HDDs, they are likely not computing the expected value of their time properly. You cannot compare the price of an HDD today with the hourly rate of your time IF you lose an HDD in the future. You need to compute the value of your time IN EXPECTATION, provided that you lose an HDD of data. In many cases, it probably comes out a lot closer than you might think.
For example, I tend to rip blu-rays into MKVs without any additional compression, and I store an average of 80 MKVs per 2TB HDD. Using MakeMKV, it takes less than a minute of my time to rip an MKV (I typically do it when I am using the computer for other reasons, so it literally takes less than 1 minute of my attention to do the rip). Currently, I have 4 HDDs with movies on them. If the annual failure rate of the HDDs is 5%, and I replace them every 2 years (I'm always upgrading stuff), then the chances of having no HDDs fail in any given 2 year period is 66.3% (0.95^8). That is a 33.7% chance of 1 or more HDDs failing in that period (1: 28.7%, 2: 4.6%, 3: 0.3%). If I value my time at $100 per hour, and it takes 80 minutes of my time to replace the MKVs on an HDD, then the expected value of my time required is $133 x (0.287 + 2*0.046 + 3*0.003 ) = $51.60. So it is not even worth it for me to add a single parity disk, since the 2TB drives cost more than $51.60.
Of course, as the number of disks go up, the chances of a failure go up quickly. So somewhere around 5 or 6 disks it is going to be worth it to add a parity disk. That is easily done with FlexRAID.
But it is difficult to justify creating a completely separate backup server for movies, unless I think the chances of my current backup server being totally wiped are high. If it costs $500 + cost of HDDs to make a server, and $133 of my time to re-rip movies per HDD, then the relevant comparison is $500 + C * N to P * N * $133, where C is the cost of a 2TB HDD, N is the number of HDDs with movies, and P is the probability of losing all of the movies on the server. If N = 16, C = $80, then the critcal value for P is 84%. As long as the chances are lower than 84% that I will lose all the movies on the server, it is cheaper to not use a separate backup server for movies.
Note that this analysis does not apply to hard to replace files, like personal files or pictures I have taken. If I lose those without having a backup, then I cannot recover them, ever (well, maybe a drive recovery service could do it, depending on the type of loss, but even that is iffy). That is why it is a good idea to separate those types of files from the easy to replace files.