>The MAGA platform is associated with explicitly barring some of them from the country.
That's essentially saying that people have to agree with the whole platform or none of it.
As an example, there are many liberals who voted for Obama and did not agree with all aspects of the platform (healthcare reform or military policies). Would wearing a "Yes, we can" shirt/hat be offensive, then?
That kind of argument seems very reductionist.
Finally, the very format of your question is problematic, for two reasons.
First, making claims that someone is trying to offend by wearing a slogan is what is referred to as "attribution of intention". Instead of having a dialog about it, you're concluding the person's intention. As someone who has often been on the receiving end of that (I'm sure we all have on divisive issues), that is very offensive.
Second, this type of reasoning is what I often call, "From ignorance comes uncertainty." You are indirectly admitting you cannot understand any other reason someone would act in a certain way, and then imply you know the "true" reason.
Usually such statements are phrased as "I cannot think of a good reason X would do it, therefore it must be because of Y".
I'll grant that you did not use this exact template, and if your question really was borne out of curiosity, I apologize for my own "attribution of intent". But I do hope I have given you something to think about on the topic in question.