First you need to decide what you want to consider a hybrid python, is it one that is cross between differant genus, species or races, differant locailty types, differant genotypes or even a back crossed animal. There are all sort of arguements that vary according to what you are talking about.
At the genus crossing level(not sure of technical name), many would argue you are playing god, messing with nature etc. and possibly creating combinations that dont work well, which is a possible cruelty issue. Those that do it would say they are creating unique snakes that can look good. Im not sure if cross genus hybrids are likely to be fertile so tainting breeding lines probably isnt an issue with these sort of hybrids.
Interspecific hybrids are crosses between differant species, they can be fertile in some cases eg. carpet X GTP but im not sure how common this is. Many would also argue this is playting god etc. and it does have the potential to taint pure lines. It can also create differant unique looking snakes.
Intraspecific hybrids are crosses with in a species, as far as i understand generally considered to be crosses between differant races/subspecies. Again you get the same palying God arguement(though probably from much less people) and a high risk they can contaminate pure lines. They can be used to transfer expensive traits between differant animals and also produce differant looking animals, although many can look similar to either parent and easily blend into a pure category if honesty is lacking. These hybrids stronger(probably not the best word) due to heterosis or hybrid vigour. However its hard to consistantly breed hybrids to look similar, which isnt favourable when trying to line breed stuff to all be a certain way that is easily reproduced.
Then there are also hybrids that are simply crosses of genetically differant animals that can be the same taxa. This includes virtually all breeding so is usually not the common use of the word by the general snake keeping public.
In most cases arguements against are purely sentimental although if a stronger animal is produced it may cause ecological or conservation issues if a wild population is formed. Arguements for hybridising are genreally limited to creating differant looking pythons.
That is my basic understanding anyway. Anyone feel free to point out anything that is wrong or add things i have missed.
