Tosfos write [שבת ק"ו. ד"ה וחובל] that מלאכת חובל [wounding] must be לגופה [for the sake of the blood] but if he doesn't need the blood, such as if the blood is אסור בהנאה, then it is called a מלאכה שאינה צריכה לגופה and permitted [מדאורייתא].
However, if a person didn't know that the blood was אסור בהנאה it is considered צריכה לגופה but nevertheless he is פטור because he is מקלקל [destructive], since למעשה he has no use for the blood and can't give it to his dog [he lives on the Upper West Side where there is a 5-1 ratio of dogs to people].
Now let's see - said HaGaon Rebbe Avraham Genechovski! Even in an instance when it wasn't originally אסור בהאנה, nevertheless it may be permitted to use because it was extracted with a מקלקל - for if מלאכה was done בשבת the מעשה שבת made it אסור and if so it is מקלקל [if he could only give it on Shabbos when it is still אסור]. However, if it was מקלקל then it is not אסור because of מעשה שבת - and if so it is a תיקון. And if it is a תיקון then it is אסור because of מעשה שבת in which case it is מקלקל and thus מותר. Ahhhhh - מותר? Then it is a תיקון and thus אסור.
And round and round and round.... 💿💿
