GPLv3 has an elaborate preamble, which should be able to answer some of your questions. In particular, wrt "whom are you trying to prevent from using this", it mentions things such as:
we wish to avoid the special danger that patents applied to a free program could make it effectively proprietary
and:
if you distribute copies of such a program, whether
gratis or for a fee, [...] You must make sure that they, too, receive or can get the source code
So, given that the GPL says these things, and the author has selected the GPL for this project, by a reasonable guess the answer to your question is, "people who would otherwise do/not do those things".
Rather than adding a TODO item onto the list of the person who has already gifted this to us, where that item would involve the labor of enumerating over a set of scenarios, composing a response to you, and hoping that it answers your question, how about helping both them and yourself by inverting the workload and elaborating on what you mean?
GPLv3 doesn't prevent anyone from using the covered software. Who do you think is prevented from using this? Do you consider the GPL to be a bad choice for some other reason, and you think there is a compelling reason to do something else? What are those reasons?
And ultimately, this is software that is being provided to you, generously, at no cost, and the author has gone out of their way to let you do stuff with it that you otherwise wouldn't be able to do. If it doesn't suit you and you don't want to "give more of a look into it", then don't.