The male Cannabis plant gets a bad rap with many people, hence its caused the creation of the feminized seed industry. While there may be some practical and useful reasons for feminized seeds for many people there are some draw backs that don't commonly get discussed.
Firstly so everyone reading this is on the same page I want to list and define some botany terminology:
Dioecy or being Dioecious: The characteristic of a species having a distinctly different and separate male and female organisms (i.e. male and female flowers on separate plants).
Monoecy or being Monoecious: A single organism possessing both a distinct male and female flower at the same time
Self-incompatability: This is a common 'mechanism' of flowering plants that prevents them from being pollinated by themselves in favor of out-crossing to preserve some form of genetic diversity.
So Cannabis as a plant is primarily Dioecious, male and female (already rare) but it is also capable of becoming Monoecious, male and female flowers on the same plant (more rare) when stressed or when Males are not available.
Many plants that are Monoecious have the trait of self-incompatibility, or for example Avocados which have a single flower that for a period of time is male and puts out pollen, then turns female later on to receive another plants pollen.
Why are there all these anti self pollination mechanisms you might ask well, because if a plant becomes pollinated by itself, its seed offspring will be the genetic clones of itself which result in a lack of diversity as well as the high potential for mutated or undesirable recessive traits to become prevalent thereby weakening the plant in the future.
Cannabis has either lost its ability to prevent self pollinating, or didn't have it to begin with so that aside how does it work? Genetic testing has shown us that the male Y chromosome (which has two arms a long and a short) binds to the female X chromosome on the short arm. This is significant because the male associated genetic marker is located on the long arm of the Y chromosome, which explains why a female "Y" gene can successfully bind to a true female X gene, as the marker for Male does not make contact. Ref-A1
This could have simply happened purely randomly or was perhaps (and more likely) spurred by environmental stresses that prevented male pollen from spreading and fertilizing female flowers. Either way, this is clearly meant as an extreme/adverse condition survival mechanism to prevent the species from completely dying out.
So...what happens when you force such a mechanism to be expressed, repeatedly? well primarily you lose diversity pretty quickly, which to many who enjoy a specific strain of Cannabis and its traits might appear to be a bonus but you also weaken the plant and increase the chances of adverse mutations occurring through lack of genetic diversity. Ref-B1
In contrast with a selective breeding program you can still preserve your desired traits, it might take a few generations of plants but then you have a much stronger and healthier plant for the future, as well as the possibility for new random expressions that could be even better i.e. a new phenotype.
Let's look at an example: Bananas, specifically the common yellow 'Cavendish', they have been mass produced from clones which is essentially the same thing as a self pollinated "feminized" female cannabis plant.
The Cavendish is the 'classic' yellow banana you see everywhere however they are entirely vulnerable to a fungus (fusarium oxysporum) born wilting disease that kills them and spreads very easily. They have no resistance to this and attempts to stop the outbreak of this in Asia have been unsuccessful. All it would take is for this fungus to spread to the other locations where Cavendish bananas are growing and they could all disappear. Which as it turns out has happened before with the Gros Michel or "Big Mike" banana variety which nearly went extinct in 1950 except for a few small isolated areas, which was when Cavendish bananas replaced that variety. Currently the only remaining wild banana plants (which there are only a handful of left) are on the isolated island of Madagascar, which researchers are hoping to breed with the Cavendish to increase genetic variety for a chance of developing a new banana strain with resistance to this fungus based disease. Ref-A2
So its not a stretch to imagine that in the future if feminized plants are allowed to take over, we will continue to lose genetic diversity as they WILL at some point be crossed with each other in attempts to get new genetics. The more times these crosses happen, the more similar all the remaining plants will become, the possibility of losing the male genetics is there as well and once its lost you can't get it back.
Imagine a future where there is so little diversity in Cannabis plants that given the rise of a destructive and highly resistant fungus, it could be all but entirely wiped out. No more Cannabis for anyone then along with all its benefits, except maybe synthetic pharmaceuticals and we all know the problems with those.
Just in case genetic diversity and overall plant health aren't good enough for you, here are some other interesting facts about the male Cannabis plant.
1. Male plants also contain CBD, THC, Terpenes (everything the females contain, just in lower levels) So not only can you still use the males and or make extracts (CannaButter), there's no reason why it isn't possible to selectively breed males for higher THC or CBD content as well. It's simply that no one has really done it since it was primarily believed that only females contained active compounds. Thus "not being able to get high" from a male is a myth. Ref-A3
Also due to the differing ratios of cannabinoids, there is anecdotal evidence out there to suggest the effect is more ‘high’ than ‘stoned’, and can be enjoyably cerebral. Ref- A4
There's also the high likelihood for male plants to flower, and therefor be harvested faster than females. Ref-A5
2. Anecdotal/historical wisdom states that male plants although not as strong as female fibers, have finer more flexible fibers (and produce more of them by up to 30%) than females and are thus capable of producing 'higher quality' and softer or 'finer' textiles.
3. You can use your male plants for eating/juicing to get additional health benefits from consuming fresh greens. (Or shred the fresh leaves to use as top dressing then water to act as a natural nitrogen booster/fertilizer for your females, or just mix the mashed leaves with water, strain out plant material and use as a tea).
4. You can rather easily and efficiently produce your own seeds with males, and no longer be dependent on buying seeds from an outside source.
5. Again, you are helping to preserve the entire genetic makeup and ensuring the long term survival of your favorite plant by keeping male genes alive.
References:
Ref-B1:
https://phys.org/news/2015-01-affirms-sexual-reproduction-mutations.html
Ref-A1:
https://www.ncbi.nlm.nih.gov/pubmed/11202435
Ref-A2:
https://www.bbc.com/news/science-environment-44712034
Ref-A3:
https://www.unodc.org/unodc/en/data-and-analysis/bulletin/bulletin_1971-01-01_1_page006.html
Ref-A4:
https://sensiseeds.com/en/blog/males-useless-think/
Ref-A5:
https://dev.purduehemp.org/hemp-production/