Holding never affects the price of anything. If there is a day, when billion people own something but only one sell and one other byus, those two will create the price.
Holding definitely affects the market. Holding basically means that the coins are being kept away from circulation, and thus off the market. The more people end up holding, the lower the number of circulating coins will be, and that will reflect on the market. If no one was holding their coins, everything would eventually end up flowing back into the market, which would then result in a situation where there is far more supply than actual demand. If we look in general, the number of on-exchange coins has only been going down throughout the years, and this is something that will continue to happen. It's a slow process, but it has definitely had a major impact on the market.
If you think the opposite of holding is selling on the market (simultaneously), only then you are right. You could also think that opposite of holding is ...
1) Using bitcoins to buy commodities. That would not have negative impact to the price of bitcoin.
2) Not have bought bitcoins at the first place. That is the most common behavior among humans, and doesn't affect the price unless they are some celebrities talking publicly about it.
3) Short-selling and yes, that would have a negative impact.
