Let's discuss cruelty when it comes to keeping the fry alive.
In the wild, the most deaths of fish happen within the first few weeks of life, while they are fry. This is why your guppies have so many, to try and ensure that at least some make it. When you take them out of that situation, the guppies still make a ton of fry, only there is nothing killing them. Which is not only unnatural, but now the fish are living in bad conditions. Now, you have way too many fish, having bad living conditions, all because you don't want to duplicate the natual settings for the fish.
My advice is simple: if you won't replicate nature as much as possible, then replicate it the least amount possible by removing everyone of one sex and sell the excess. If you don't want to allow the natural setting to happen, then make sure your fish are happening by removing what is causing your "problem".
In the wild, the most deaths of fish happen within the first few weeks of life, while they are fry. This is why your guppies have so many, to try and ensure that at least some make it. When you take them out of that situation, the guppies still make a ton of fry, only there is nothing killing them. Which is not only unnatural, but now the fish are living in bad conditions. Now, you have way too many fish, having bad living conditions, all because you don't want to duplicate the natual settings for the fish.
My advice is simple: if you won't replicate nature as much as possible, then replicate it the least amount possible by removing everyone of one sex and sell the excess. If you don't want to allow the natural setting to happen, then make sure your fish are happening by removing what is causing your "problem".