I have seen some messed up misunderstanding of becoming one, but this takes the cake... I'm not a psychologist but I think he's got actual issues. Relatively harmless with a little supervision, but still.
Why people find this strange ? It the same as sniff in your crush cloth and stuff and even lick some dirty part. They both dirty but that it, it more about sexual appeal.
I don't see anything serious will be a big problem here. there is even someone bring up Silence of the Lambs to compare ?
This likely is not as weird as it seems. Humans do not molt, so it is disturbing as it is easily interpreted as wearing human flesh. Maybe to her it is more like wearing a full body suit that closely looks like you. Still somewhat creepy.
It seems like they discovered next levels of striptease and crossdressing - molt play. Nice job, perverts)
And I hope MC doesn't end like dollf*cker from Ibitsu, despite they looks kinda similar.
Funny how many people missed the part where too much glue came out, surprising the MC. He doesn't glue her molt to himself on purpose. The author obviously meant it as an accident. The visual did go overboard, admittedly.