Comments:

The article opens with a comparison of the incidence of inflammatory bowel disease in Alberta Canada vs. a county in Minnesota.  This is a peculiar comparison. It provides a dramatic set of numbers but no reason why we should consider these two population groups comparable.  They are not geographically close.

The article cites a paper published in the Canadian Journal of Gastroenterology is an opinion piece and not a scientific study.  

The article cites  a 2008 study published in the Journal of Toxicology and Environmental Health studying the effects of Splenda on rats. This paper was later discredited by an export panel that found the study "was deficient in several critical areas and that its results cannot be interpreted as evidence that either Splenda, or sucralose, produced adverse effects in male rats, including effects on gastrointestinal microflora, body weight, CYP450 and P-gp activity, and nutrient and drug absorption. The study conclusions are not consistent with published literature and not supported by the data presented." (Regul Toxicol Pharmacol. 2009 Oct;55(1):6-12. Epub 2009 Jun 28.) (http://www.ncbi.nlm.nih.gov/pubmed/19567260)

Mercola claims that sucralose is more like DDT than sugar.  This claim can't be assessed because it isn't backed up with any detailed discussion of the relevant chemistry. "It could easily be likened to eating an insecticide…"  This isn't really saying anything.  It's sounds sensational. Where's the proof?

Mercola's discussion of common side effects relies on anectodotal reports of people posting on his website.  This is a not a scientific basis for claiming either the causality of a side effect or the actual prevalence in the general population.  Some self selection bias exists -- Mercola's website reader's are likely already suffering some illness, malaise or have a health concern and read his pages looking for solutions.

Claims of side effects discovered during scientific studies are not backed up with citations but nevertheless Mercola says these were "ultimately dismissed".

The article is wide ranging, taking a discussion of Splenda and introducing unrelated topics (coffee, cocaine, proprietary diagnostic tools). This review is limited to examining the specific claims of Splenda toxicity. The article does not present any evidence that Splenda is toxic. 

Mercola's writing style is very informal and prone to hyperbole but he is careful to use soft language around specific health claims. The use of the word "may" softens almost every claim. It appears 11 times in this article, hardly a writing style appropriate for something based on fact. For example:
  • A paper published in the Canadian Journal of Gastroenterology theorizes that ...
  • ...Splenda may be a culprit in the rise of inflammatory bowel disease…
  • … this may help explain the pronounced increase in IBD in Canada …
  • … If you add sucralose to an already unbalanced intestinal tract, health problems are very likely to ensue… 
  • … the long-term damage of Splenda consumption is largely unknown…  [In fact you could rephrase this as "there is largely no known damage from long-term consumption of Splenda"]