It's hard to divorce my thoughts on this from the subject matter involved, but my feelings on this are mixed.
On the one hand, license plates are not bumper stickers, but are issued by the state government. As such, they have the right to decide what messages they are willing to have on them, as such messages carry an implication of the government accepting or sponsoring them. (If that were not the case, then why would the SCV be so insistent on having their own specialty plates, vs. again, a bumper sticker with whatever the heck they want?)
If the state has the right to restrict what gets spelled out on a vanity plate, it would seem to me they have the right to decide what organizations or logos get put on specialty plates.
On the other hand, I can't help but think of the analogy to the courthouse lawn. The government is presumed to have a certain sponsorship of such messages, which is why they tend to be (in court rulings regarding religious displays) a matter of all or nothing: either the government allows nobody to post messages there, or they have t let everyone post them. Allowing viewpoint discrimination in such a case is generally not allowed.
My sense is that the SCOTUS ruling here is probably the correct one — but that it opens up much more scrutiny for the basis or guidelines upon which it discriminates against particular viewpoints But I'm open to persuasion one way or the other here.
(Actually, this points up for me the folly for states of having specialty license plates in the first place.)
Supreme Court says Texas can keep Confederate flag off license plates
The Supreme Court has freed states to control what appears on their specialty license plates, ruling ;Thursday that Texas authorities were justified in refusing to issue a plate bearing a Confederate battle flag.
Americans United is decrying the ruling, suggesting that letting the state decline license plates because some might consider the message offensive might allow states to discriminate against religious groups that some find offensive. https://au.org/media/press-releases/supreme-court-made-the-wrong-call-in-texas-license-plate-case-says-americans