What am I ruining?

I have been feeling guilty about not writing more consistently. Writing for me is not easy. The words I need to express my thoughts and ideas and feelings don't always come quickly, or when they do they don't always make sense. Writing is time consuming to make it make sense and I want to do a good job, especially since I am publishing online.
I have been reading blogs for over 10 years (if you count Wil Wheaton's blog) and have learned SO much from them, but I have been so intimidated to try writing myself. I agree with Dean Shareski that sharing, even when it sucks, is important. And I want to have an online presence. I want people to be able to find my work and ideas online. My family, friends and colleagues all know about my ideas because I don't hesitate to share with them verbally, on Facebook or through a quick email, so why is blogging so hard for me to do?
This question has been nagging at me and I have been giving it a lot of thought. Of course there are the excuses like I don't have time (I finally finished my report cards) and I didn't feel well (I think I have had a cold for three months) but those really are just excuses. Then I started thinking about my writing through school. In elementary I loved writing and excelled in it. I was chosen from my school to participate in a two day writing workshop where our work was eventually published (this was a big deal pre-Internet). Then I went to junior high. And I remember two teachers in particular who destroyed my love of writing and all things language arts. Writing became a chore. It was homework and I suddenly didn't do it very well because I started to get poor grades in ELA. Thinking that I couldn't do it well made me not want to do it at all. Of course I made it through high school and university so obviously I improved, but the enjoyment never returned.
Joe Bower wrote about his concerns about reading being ruined for his daughter now that she attends school and is being subjected to a reading incentive program. But what about writing? or math? or music? Isn't everything at risk, especially with grades? As a teacher I now ask myself the question, which kid in my class am I ruining this for? And it terrifies me when I have to give a poor grade for something because what if that makes them hate science or learning or taking risks or whatever. Is it worth it?