-- Why IT must be in English? --

Why Mahathir insists on using English for math and science?

Because globally people use the English as Information Technology language at this moment.

How dangerous it is if we were to use these words in Bahasa, especially in schools.

See example below.

Hardware = barangkeras
Software = baranglembut
joystick = batang gembira
plug and play = cucuk dan main
port = lubang
server = pelayan
client = pelanggan

Try to translate this:
ENGLISH :
"That server gives a plug and play service to the clients using either hardware or software joystick. The joystick goes into the port of the client."

BAHASA :
"Pelayan itu memberi pelanggannya layanan cucuk dan main dengan menggunakan batang gembira jenis keras atau lembut. Batang gembira itu dimasukkan ke dalam lubang pelanggan."