Quote from hlpsg:
I put out this thought for critique.
If everyone tries to enter a spread order at the same time at the same number of days, you get high demand for certain strikes that you're going long, and the IV pumps up, so you buy a more expensive option.
Same thing goes for the short strikes, you all try to sell the same options, IV drops, you get very little for it. So overall, the credit you receive decreases.
If enough people do this, will there come a time when it's just not worth doing anymore?
What you say is true, of course, but the calendar spread is typically ATM options which have the greatest demand from every trader who does options, regardless of his or her system. Even investors with primarily stock positions use atm options for a hedge.
I don't think calendar spread strategy will "spoil" itself as a strategy because of the inherent demand for ATM options outside of that strategy.
Finally, even within the universe of options only traders, most of them are direction oriented, while the long term nature of calendars would not suit their trading style.
I just don't see it happening.