It is an absolutely valid comparison, imo. Some people say that day trading is similar to gambling only if you trade "without knowledge". But, firstly, there are gambling activities where skill/knowledge is involved; and secondly, c'mon, who on earth trades "without knowledge"? I personally know a trader who's losing money almost each time he trades, yet he considers himself such an expert that he's trying to teach others.

In short, I would compare day trading to skill-based gambling like sports betting and poker. Yes it's not a pure game of chance, but you can still get addicted to it.