A lot of people said that when Bitcoin dropped to $10,000 from $20,000.
Another group said the same when BTC dropped to $5,000.
While it is true that the current value seems low because of its ATH, I will never be certain that the price will never be this low again in the future.
If the price drops lower to say $1,000, many people will also say this line "This opportunity will not last forever because the market will certainly have to recover and make another bull run" or something that is similar.
You have well express your points and it is very unique especially to the guys who thinks that the bear run is an open opportunity to buy more coins; unfortunately, like you rightly explained, Bitcoin or some altcoins may one day drop to less than a dallar and many will also say it an opportunity to buy.
I have in many post topics stated that there are no particular price that may not be an opportunity, it all depends on individual assessment of falling prices in as much as one is willing to buy at a particular time. If bitcoin drop futher, for instance, to $200, many people will still say the same thing, and goes on like this, may be when Bitcoin fall to less a cent.