The title said it already, some people argue that they are just gambling for fun and that they don't gambling because they want to make money from gambling but sometimes people that makes such kinds of statement still get addicted to gambling. Is it normal?
No it is not normal. If you are gambling for fun then you have no business getting addicted. If it is fun, you just enjoy it and not counting losses or win.
Though, you are under-estimating how easily could someone get addicted to gambling even though they started within the world of gambling just to have fun and entertain themselves in their spare time.
Have you experimented something like it? getting hooked to an specific game when you initially just wanted to try it for a few rounds?
There are addicted people out there who started their experience on casinos with no intentions to earn extra money and now they are addicted, mostly because they started to chase losses and cannot let go those bucks.
We all are human beings and we can fall for addictions like that at any time.