You just made two very strong numerical claims, and yet I see no calculation or sources at all.

People have made exactly the same argument about the climate emergency. "The atmosphere is really big and humans are small, so..."

Let's see your numbers, please. Numerical claims without any form of calculation are... ah, very close to being deliberate untruths.

One or even one hundred turbines are no doubt no problem.

Japan alone would need hundreds of thousands of these to make any noticeable difference to them, five million turbines to cover their electrical grid today.

Let's see your numbers. How much power is there in these currents? What percentage would be extracted per hundred thousand turbines? What percentage of that energy will be wasted as heat?

We can't keep expanding our huge construction projects into all parts of the world in order to desperately suck out resources. Degrowth is the only answer.