If you get an ammonia liquid tester, you'll find these members are right. Test the water every day, and after a week in a less than a gallon tank, the ammonia will be off the charts. Every time a fish breathes, it excretes ammonia from its gills. It's sort of similar to locking someone in an airtight room for a week. that air will get stale fast, and dangerous (to humans) in little to no time at all. The funny thing is the air LOOKS clean and good to breath, right? Seriously ammonia is dangerous stuff. Would you want to be breathing it your whole life?
I doubt any of us are more than peeved at you for not listening, but I wouldn't push it. We want our fish to thrive ,not just do better than before. In my honest opinion, when you get a pet, you better have the resources (time is a resource as well) to make that pet's life as good as you possibly can. I'm not saying you need a 10 gallon for one fish. I'm not saying you have to constantly be worrying or thinking about the fish and its well being 24/7, all I'm saying is give him room to explore, he's the one stuck in the tank all his life, no? Give him a heater, wouldn't you want your internal temperatures to be where they ought to be? Keep his water clean.