Question: I find myself using these words *all the time*. 

Now (<-- there's one!), to be clear the context I'm using them is in conversational style writing, on social commentary, or in forum posts like these. It's not formal academic writing, and it's not story telling. (In a fictional story, these words would be perfectly appropriate if used by a character). 

Here's an example where I've used it recently:

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> Point four, I think it is realistic that people would have this interpretation. **So** on this point I'll just stress that this blog post is not intended to be malicious or make anyone feel bad. It's more an interesting exploration of social interaction and how best react and navigate it. 
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My question is - is this actually an effective writing style, in the sense of being easy to read and persuasive, and if not, how do I get around it?

Answer: 
I don't think soften is quite the right word for what these kinds of words do, nor is filler. I think of them as signal words. They indicate to the reader what direction the text is about to take. They are like the curve signs on the highway. The signs don't make the road curve. In this sense they don't add anything. But they alert the driver/reader that a curve is coming, which helps them avoid ending up in the ditch.

The most common example of a signal word that I can think of is "but". But and and actually mean exactly the same thing:

```
Tom went to school but Jane went home.

```

Means exactly the same thing as:

```
Tom went to school and Jane went home.

```

In terms of the information conveyed, these two sentences are identical. The use of but as the conjunction simply signals that there is going to be some significant difference between the phrases it joins. It does not create the difference and is not necessary for the reader to understand the difference, it simply prepares the reader for the possibility of the difference. Such words are part of the ergonomics rather than the semantics of language.
The answer to your question is yes, it can be an effective writing style; I myself do something similar when writing letters. It can come across as if you're in the room with the reader, talking to them.

My personal experience is that they should be used sparingly, however. When every second or third sentence is a so, therefore, now, or an anyway, it becomes noticeable and annoying.

I would also argue that it's not just these words that create a conversational tone, it's about writing in an overall style that is clear, concise, talkative and informal. For example, using contractions helps to create this impression, as does writing in the first person, and addressing the reader (or the person you're replying to). These are all the hallmarks of having a conversation.

The word "filler" in your subject is a dead giveaway that you're looking at these words in the wrong light. The old adage of something is perfect because there is nothing left to take away applies here. Words are not meant to be filler. If a word is superfluous in conveying what you mean, why bother using it at all? Rewrite the text without the word in question, and see how it looks:

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> Point four, I think it is realistic that people would have this interpretation. I'd just like to stress that this blog post is not intended to be malicious or make anyone feel bad; it's more an interesting exploration of social interaction, and how best to react and navigate it.
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Always aim for clarity and simplicity. Write, and then edit, edit, edit.