As long as you just think about that person or the committed act while writing and use those thoughts to generate emotions that you can put into writing as realistically as possible it's not a bad way to write. But as soon as you start creating characters that are physically and emotionally identifiable to real people you open a Pandora's box better left closed. There is probably a good reason why fiction works have that big disclaimer that says any similarity is purely coincidental and unintentional and I would never think of doing that, etc, etc,.
Just some physical features would be similar and emotionally he would be different than that person in real life. Only similarity would be that they are both bad people or as some of you put it "may of done bad things but we don't know for sure if they are a bad person" and have similar looks. that is it.
Although many great writers have based some of their characters on real people, there is a big potential problem with basing characters on people we know, especially if they are people we don't know very well or people we've had bad experiences with, and that problem is that we may think we know that person's motivations and can use that knowledge to make the character more realistic, but we may not know as much as we would like to think. We can never really see what is going on inside a real person's mind; we may make a good guess at what their motivations are, why they are as they are, but it will still be a guess. And say that I were a woman who had been through a nasty divorce and decided to use my ex-husband as one of my characters. I'd be so intent on presenting my own view of what happened between us and justifying my own actions, I could never give a truly fair representation of my ex- or why he did what he did. Even if he genuinely was an awful person and an awful husband and I was the most fair-minded and perceptive person in the world, I could not remove myself from the situation to that extent. ( Although, it's true that I might create a convincing portrait for fictional purposes.)
Whereas with wholly fictional characters that we create—taking a bit from this person and a bit from that person and maybe something of ourselves and some attributes we don't even know where they came from before they popped into our minds—such characters as those we CAN know from the inside out, because we created them. We know who and what they are, why they did what they did, why they didn't do what they could have done, how they feel about it afterward, what they are likely to do next, etc. etc.
Well Teresa, I think I have to explain this a little better to you. I wouldn't actually be basing a real life counterpart to that person like the same name, same background, same voice, same dress style, same home, same favorite food, same favorite intercourse position, etc, etc, etc. There would be ONLY just a few slight resemblances like the facial features, looks and expressions with only emotional resemblance is that they are BOTH responsible for doing some kind of wrong, but they are not the same person. Just in my mind or only in my head would only I see them very similar I'm basing some characteristics off of them. Not an identical cookie cutter image which would be too obvious.
Here let me give you an example of the real life person. I mean an actual REAL LIFE example, this one is not made up and really happened.
I'll even use a fake name and fake location just to avoid any kind of problems. But let's PRETEND that's his name and name of the town.
John Joe was actually a pervert in real life who spoke with a scratchy voice and had a pointy long noise, quinty eyes and small mouth, always wore a patterned tie with dark blue pants and worked in at a school church. There were many times he had sexually and physically abused me as a child growing up, causing me pain physically, emotionally and chronically in many ways and even tried to convince me to become gay at the after school church activities. He had done this abuse to other children in the past, both males and females in our hometown Stupidville Lane. Although I still don't know the extreme he went with them, he sure went far enough with me, even manipulating me so I would not take it as it was a bad thing at the time. He had continued through life to be verbally and physically abusive to other people, especially women and had even spread hateful things about me and about others who he did not like and he would always cause people to fight with eachother, even threatening me with bribes in case I would ever try to testify and confess in court and when I did try to speak, it was difficult to do anything about as it had been years passed that incident which was too long ago and the others that it happened to have moved away ever since then and were no longer around to confess what had happened.
Now here's my made up example of a FICTIONAL version of that. The year was 1670, Captain Cramble was a savage and ruthless pirate with a deep scary voice, had a pointy long nose, mustache, squinty eyes and very small mouth, wearing a long doublet coat and monmouth cap who had murdered and robbed countless ships and caused fear and terror across Margarita Island and also recruiting and kidnapping children from families, raising and manipulating them to do his dirty work as murderous thieves. A vicious and manipulative man that was known for and his ruthless ways but was an actual coward that hid behind his brainwashed men to do the fighting for him. One man, one shrewd, heroic, brave hero decides to take a stand (becoming a leader) and put and end to this monster that terrorizes the sea and families homes.
Now did I use John Joe's name? Did I mention that he had raped or sexually abused this specific person and countless others in Stupidville Lane? Did I mention he taught at a school church? Did I say he has a scratchy voice? Did I mention he loves to wear dark blue pants and a patterned tie? did I mention him spreading hate about anyone or any specific bribes? No. They are both two different people with just a few "coincidental" similarities.
This is the point I'm trying to make and I think some of you are taking this the wrong way as if I'm going to create the real life story of John Joe and write a book about him and myself.