- Is there any argument against this?
- Which one should be the main tag?
I would argue that bioinformatics and computational-biology are actually different topics but in the context in which they are used here, it is more likely to be bioinformatics.
Bioinformatics would consists of most data analysis and data-mining. I would draw the line at biological simulations like folding@home and systems biology and define that as computational biology. However, none of the questions tagged so far fall under those categories.
I'm in favor of merging them. There is no single definition for either, nor a clear delineation between them. Compared to other areas of biology their overlap is so large that the tags should be merged.
I'm less sure about the main tag, but I guess bioinformatics is more popular (and succinct).
I guess there isn't much point to comment on status-complete, but for posterity I disagree with this decision.
Bioinformatics and computational-biology have distinct communities, there is a lot of overlap but there are many researchers whould identify with only one of those groups. The arguments given in the other answers of "there hasn't been a distinguishing question, yet" is not a valid one. From the little I've read of bio.SE there are almost no mathematical or computational questions in general. You should not judge on the criteria of existing questions as much as on the criteria of possible future questions.
For instance, I recently asked a question:
Which I think fits under computational-biology, but in my opinion definitely does not fit under bioinformatics. Since the tags have been synonymized and I didn't want bioinfo as a tag, I could not tag this question as computational. But I did find other tags (like mathematical-models; although I maybe should have created a computational-models tag) that worked.
Both "bioinformatics" and "computational-biology" are different as aptly answered here: Is "computational biology" different from "bioinformatics"?