I have a doubt , please only respond if you know what youre talking about . I beleive that bitcoin to usd price is stucked cause of all the alts coins that are pulling it down , if bitcoin rises an 20% againts usd , all the coins rise as equals. If bitcoin falls all the coins falls againts usd.
The vast majority of alt-coins have their value determined by BTC value. With the exception of LTC and a handful of other alt-coins, there's no direct means of converting fiat into these without having purchased BTC or LTC first and then exchanging them for the alt-coins. In other words, if someone wants to buy an altcoin, they more likely than not will have to buy and sell through BTC to get there.
As with any other market, speculators will throw down money in related commodities/companies/goods whenever there's a rise in the value of the primary item. It's possible that alt-coins are somehow impairing BTC, but I don't think this is a valid reason.