In Istanbul public transportation is free for people older than 65, and also for disabled people. For students between 7 and 30 years it is cheaper; 41% of normal price.

In Turkey, 65+ and disabled thing is mandated by central government. Only student discount is decided by the municipal authorities.

Why is it seen negatively?

Making things free can increase demand beyond what’s reasonable (for example, there was recently someone in the press explaining how, thanks to moviepass, he would enter a cinema just to go to the restroom). Maybe old people take trains just because they can, taking capacity from paying customers that really need the train to get to work or whatever.

I've seen that. In my small town, taking the bus is free for senior citizens. So they sit there all day and socialise because they simply have nothing better to do.

There is an entire community of homeless who ride the all-night VTA buses across Silicon Valley.

VTA likes this because it artificially inflates their census.

Because only a few people truly understand economics.

As far as I can see, highly intelligent people of roughly equivalent intelligence/experience disagree profoundly over economics. So I doubt anyone truly understands economics.