The "hazardousness" of artificially made sweteeners
From the NHS website in the UK: 
The US National Cancer Institute conducted a study of nearly half a million people, comparing those who consumed drinks containing aspartame with those who did not. Results of the study found aspartame did not increase the risk of leukaemia, lymphoma or brain cancer."
Also:
In 2013 the European Food Safety Authority (EFSA) conducted a comprehensive review of the evidence (there is a pdf on the website) and concluded that aspartame was safe for human consumption, including pregnant women and children.
Cancer Research UK also have stated that artificial sweeteners are safe. 
Rigorous testing is carried out before a sweetener can be approved for use in the EU.
So, no evidence of cancer in humans. Rats, maybe. Humans no.