You are right about this, we are too focused on holding that is why news of a big sale usually put the market in panic mode. A single sell off of 24,000 BTC caused the market to drop by $4,000 and even more but a buy of 24,000 BTC will rarely push the market higher by that amount. This simply means that people tend to panic when they hear of sell because all their minds are fixed on buying and holding. Just like you said, we have to prepare and accept the fact that people have rights to sell and they will also take profits and that will not mark the end of Bitcoin. In some communities I belong to, if you dare mention selling, you will be seen as someone against Bitcoin. This us not right because buying and selling is part of what makes the Bitcoin network strong.
You are right, I don't know which communities those are, but in this forum, most of the forum members or BTC enthusiasts don't like the action of selling Bitcoin, they are not wrong though because they are not against selling BTC but selling low. As far as I have understood their point, they meant to say, Don't sell now even if BTC is at $120k, don't sell even at $150k.
Because they are too optimistic about the price actions of Bitcoin that they have bigger targets like $500k or maybe 1 million, that is too long to get, but they are too optimistic, and who knows if in the next 18 years BTC actually hits $1 million? So they suggest anyone to hold even if they don't have BTC in their wallets, hehe.