If the futures price is $5k and the spot price is $10k, I will sell my Bitcoins in the spot market and buy in the futures market. When the trades are settled, I will buy again in the spot market, netting a neat profit. Millions of others will do this. This is one reason why your strategy won't work.
How does this affect the price of bitcoin? What you're saying seems to imply that the US$ will be affected not bitcoin. I suppose if you own a lot of bitcoin and you flooded the market just to buy the futures contract, that would tank the price?