Equally, I could always choose to do nothing, and let his second set of 31 trades do for him what they will - either make or lose him money.
Let's suppose I did do that, and after the 31 days are up, his second set of trades has netted him 310 pips - i.e. the average profit of the second trade over the 31 days was 10 pips each day.
His argument will be "see - by having to take the second trade, I made an extra 310 pips that I might not have made if I'd just closed the position".
The problem with this, of course, is that you cannot say now that the second trades over the coming 31 days will make you a profit. It is impossible to say anything about them at all, other than that they will incur a cost.
Yes, on this occasion, you made an extra 310 pips. Will this always be the case? Can you say that, on average, you will always make more money than you lose? No. What if you had lost 310 pips? would that be an argument for only trading once a day? NO.
is there anything you can say, on Day 0, about the outcome of the next months trades? NO.
It's because of that you should always choose the option with fewer costs - Trader B.
[I think where's he's missing it is that he thinks the P&L of the second set of trades comes in to the equation - it doesn't, as you well know.]