That’s a fair question. Here are my short and long answers:
Short Answer: Of course you have the right to write any way you like. However, your readers have the right to refuse to read what you write.*
Long Answer: Most of your readers – especially the smarter ones – know the rules of grammar. They assume that you know the rules, too, and that you are at least generally following the rules. So, when they notice that you are not following the rules, they conclude that reading your writing will always be more difficult than reading the writing of the millions of writers who do follow the rules. Your readers may even conclude that you routinely treat information as carelessly as you treat grammar, and therefore that you are an unreliable person. And they are likely to decide never to read anything else that has your name on it.**
Grammar is not just a bunch of rules; it is a description of how our readers think and read. Therefore it is a description of how we need to write – if we want to hold their attention and gain their trust.
The Takeaway: Yes, you can “break the rules” of grammar all you want; just don’t expect your readers to trust you. If you want to be taken seriously, write like a serious adult, not like a willful child who refused to learn the structure of his own language.
*Unless they are a captive audience; for example, if they are your employees or students.
**For example, I refuse to read the writing of hundreds of grammatically incompetent reporters, novelists, nonfiction writers, academics, consultants and columnists – except when I’m looking for samples of careless writing to analyze on this blog.