Please tell me why I should Just buy BTC and sit on them (why take the risk) 
In retrospect I should have bought BTC without any doubts.
Possibly, though in all honesty it's good to also acknowledge that you might not have held to your BTCs after they'd have rosen significantly in value. With a miner, you're (somewhat) stuck to it.
Sure you're right.
With a miner your BTCs will be "released" slowly, solved block after solved block, and you will not be able to sell all your "potential" BTCs all at once under the influence of your emotions.
Though, I wonder how high it would be the price someone is willing to pay to get this "safety" measure in place. Mine, at the end of the road, will be somewhat between 8 to 10 BTCs plus the cost of the miner (7500$), definitely a high price to pay.
Taken into account tha I've not even considered energy and maintenance costs in my back-of-the-envelope calculation.