I don't think there is much effect of forks on the price of Bitcoin.
If there is a community believing in Bitcoin and there is more than enough demand to keep bitcoin above 3K, the Hard forked coins can go shove up themselves in the asses.
What we have actually seen is that this forks loose value over time and money still returns to bitcoin.
Perfect example is BCH.
According to prices late December 2017
BCH all time high - $4000
BTC all time high - $20,000( or close to the price in some exchanges)
BCH was even the third on marketcap rankings
Current situation
BCH price - $162
BTC Price - $4024
BCH currently 6th on marketcap ranks, Almost getting taken over by Binance coin.
As we can see, In approximations, BTC price dropped 5 times for ATH in late 2017, BCH price dropped by a whopping 25 times. Where did the money go?