If you just found that out 5 minutes ago I advise you to read and think on the matter for a short while before getting angry and coming to conclusions.

A transvestite is a person (commonly a man) who dresses up as the opposite gender for a fetish or hobby. Transvestites are not LGBT and have nothing to do with this topic. You are probably thinking of the term transsexual or transgender, a rare occurance where someone's physical sex doesn't match up with their "head gender" and causes gender dysphoria.

The reason we use the term cis is because it is shorter than "non transgender" and this is common with many terms. The word neurotypical can be used to describe people who do not suffer from mental illnesses or disabilities. There is nothing wrong with having a term to describe the norm or majority for ease of grammar. These are not new terms and have been around for longer than you claim.

Again- I understand if you are a bit ignorant or scared of these topics. If you come to people with less hostility, many many people would be very eager to politely explain these things to you and help you understand. At the very least, use Google or the search engine of your choice to do quick research on these topics and terms before you formulate an opinion like this.