tWitch's widow Allison Holker says she has a good reason for blabbing to the media about his alleged drug problem ... she says she's just trying to help others.

Allison defended herself Thursday amid a barrage of online attacks from her late husband's friends and family, who are all pissed off about her recent media interviews and upcoming memoir ... where she touches on his alleged drug use leading up to his suicide.

In a long social media post, Allison says ... "I hope that by sharing our full story maybe I can help someone else who might see themselves or a loved one in Stephen."

tWitch's family and friends certainly don't see it that way ... ripping Allison for bringing up the sensitive topic in a cover story with PEOPLE magazine and adding passages from his private journal in her new book.

Basically, the family thinks this is all in poor taste and is a money grab by Allison ... and they're disputing her claims that she found a stash of drugs among tWitch's belongings ... saying he was no addict and she was the real drug abuser.

Allison address his family in her rant and says she's just being an open book in hopes of helping people catch "red flags" about loved ones before it's too late.

She also claims all the money she's making from the book is going to a mental health foundation she started in his name.