All interest is usury in Islamic Law (and the laws before it such as Christianity and Judaism). There are ways to to put free cash into productive use without exploitation.

I understand and I disagree. Interest isn't always "exploitation". A 5% loan isn't exploitation and it is very stupid to ban such things.

I think it's easy to look around us to see why it makes complete sense to prohibit it.

If going by the very poor economic performance of Muslim countries I would say interest is a very good thing if limited to reasonable interest rates and fair bankruptcy laws.

Correlation vs causation (post WWI colonization comes to mind, that continues to this day). Historically, there was a period of time when there were no poor people left to take Zakat, everyone paid their share, and no usurious transactions permitted.

Historically, there was a period of time when there were no poor people left to take Zakat, everyone paid their share, and no usurious transactions permitted.

When was this?

During the time of Umar bin Abdul-Aziz.

This is worth treating carefully. There are sources like Ibn Kathir and al-Tabari writing centuries later which claimed that Zakat collectors would return with unspent funds because eligible recipients could not be found. Even if we take this at face value, that's a leap from there being no poor people left. Did it apply to the entire empire or only a few regions? How likely was the collector to actually find recipients if they existed in a given region? etc...

Point is to refute the claim the current situation in some Muslim countries is caused by Islam, instead of it being a direct consequence of colonialism.