Simple pleasures indeed. Please realise that most of the rules and regulations imposed on you as an airline passenger are there not to ruin your fun and to be a killjoy, but so that you benefit from many years of flight safety experience that has been achieved at a great cost of lives, money, time and knowledge.
We frequently have passengers who think that for whatever reason they know better, or the rules should not apply to them as they are somehow more special than the average passenger. They may challenge a rule because they think they know the reason behind it but disagree with that reason. They generally have never even contemplated the existance of the twenty other good reasons for imposing that rule. This sort of passenger causes the cabin crew as many headaches as the drunks, disruptives etc.
You've been offered a number of reason behind the restrictions on electronics but discounted them. These are not opinions but facts. Blanket restrictions are applied to err towards safety and to be workable. We can't give dispensations to every individual who knows better or 'has a good reason' not to comply.
Your seatbelt comment is just daft and doesn't really warrant debate. You try a rejected takeoff without a seatbelt on and see how you get on. You are required to pay attention to the safety brief so it is fresh in your memory when you need it. Same reason we brief takeoff emergencies in the flight deck every time. Same reason that you as a PPL brief an EFATO before you takeoff. (Do you?) You are not as familiar with the aeroplane as you think you are.
Threads concerning the restrictions on electronic devices on flights are ten a penny. If you only found two then your search terms were too narrow.
I hope this helps you to understand the reasoning, appreciate that the compliance of passengers is required to try to maximize everybody's safety.
For a very measured explanation read this:
What Alec Baldwin doesn’t know about air travel - Salon.com
Unfortunately if you still don't like the reasons given, the bottom line is 'because we say so'. You are legally obliged to obey the lawful orders of the crew.
Finally, go to Advanced Search. Use electronics as the keyword and search in Passengers and SLF forum. You will get plenty of hits. Nearly half of them will be directly relevant to this issue.