If it was really "the small donations individuals send in which would cost more to return and probably insult people," then why does Trump have a donations page, which is prominently featured on his website?
The fact is, he is actively soliciting donations--which represent a small, though significant portion of his total campaign revenues, and which he can use to pay himself back for loans made to the campaign.
Trump has said many times that you do not need to send him donations but instead people are mailing envelopes to him with cash and checks and they were sending to any and all addresses. He probably has had to finally put a donation button on his website.
The facts are:
1. Trump has repeatedly said publicly that he does not need donations.
2. It would be too much trouble to send it back
3. So what if he does keep the money?
4. A few million dollars is a miniscule fraction of the
money Trump will have to spend to get into the WH.
Grasp at some other straw. This is a non starter.