You are free to psychologize your opponent when his position is demonstrably false or incoherent. If his reasons are worthless, then you are justified in exposing the motives that drive his commitments.
What the presentist affirms, roughly, is that only (temporally) present items exist: there are no nonpresent existents. The anti-presentist denies this, maintaining that there are nonpresent existents. Now there is no genuine dispute here unless the identity of the presentist thesis is perfectly clear and the anti-present is denying that very thesis.
Following some earlier suggestions of Peter Lupu, I will now try to formulate this dispute using the concept nonpresent existent. I will use 'NPE' to refer to this concept, a concept we may assume both the presentist and his opponents understand. A nonpresent existent, by stipulative definition, is one that exists in time, but is either merely past or merely future. Using NPE, presentism and anti-presentism may be defined as follows:
P. NPE is not instantiated
AP. NPE is instantiated.
The dispute, then, is about whether NPE is instantiated. NPE is a concept both parties understand. So it is common ground. The dispute is not about this concept, but about whether it is instantiated.
But note that 'is' occurs in both formulations. Does it have exactly the same sense in both (P) and (AP)? If not, then the common ground afforded us by NPE avails us nothing.
Yesterday (see link below) I distinguished five time-related senses of 'is.' Starting with (P), which sense of 'is' is operative in it? We can right away exclude the 'is' of atemporality since presentism is a thesis about temporal items. We can also exclude the 'is' of temporal presentness. The presentist cannot be charitably construed as saying that NPE is not now instantiated, for that is trivially true.
The 'is' of omnitemporality is not a suitable candidate either. For if NPE is not instantiated at every time, then we have quantification over times. But one cannot quantify over what does not exist. So nonpresent times exist. But if so, then NPE is instantiated, contrary to what the presentist intends.
On the disjunctively detensed reading of 'is', the presentist is saying that NPE was not instantiated or is not instantiated or will be not instantiated, and the anti-presentist is saying that the NPE was instantiated or is instantiated or will be instantiated.
Does this do the trick? At the moment I cannot see that it doesn't. But time is the hardest of nuts to crack and my 'nutcracker' may not be up to the job . . . .
I understand Aurel Kolnai has a paper on this topic. I haven't read it. But the paradox has been put to me as follows in conversation.
It is morally objectionable to forgive those who will not admit wrongdoing, show no remorse, make no amends, do not pay restitution, etc. But if forgiveness is made conditional upon the doing of these things, then what is to forgive? Conditional forgiveness is not forgiveness. That is the gist of the putative paradox, assuming I have understood it.
This is something I need to explore, but off the top of my head I fail to see a problem. The first limb strikes me as self-evident: it is indeed morally objectionable to forgive those who will not admit wrongdoing, etc. But I reject the second limb. I admit that once the miscreant has paid his debt, he is morally in the clear. His guilt has been removed. But I can still forgive him because forgiveness does not take away guilt, it merely alters the attitude of the one violated to the one who violated him.
Suppose you take money from my wallet without my permission. I catch you at it and express my moral objection. You give me back my money and apologize for having taken it. I forgive you. My forgiving you makes perfect sense even though you have made restitution and have apologized. For I might not have forgiven you: I might have told you go to hell and get out of my life for good.
By forgiving you, I freely abandon the justified negative attitude toward you that resulted from your bad behavior. This works a salutary change in me, but it also does you good, for now you are restored to my good graces and our mutual relations become once again amicable.
So I see no paradox. The first limb is self-evidently true while the second is false. Only conditional forgiveness is genuine forgiveness.
It is of course possible that I am not thinking deeply enough!