OFDM - why do we need IFFT? This question is really related to - is there any need for IFFT in the first place?

If we want to send a bunch of complex-numbers (vectors), then most OFDM discussions involve presenting those numbers to an IFFT block, and the output of the IFFT block will then have a bunch of complex numbers for which to transmit in a queued fashion through a QAM block.

Can I ask ----- is the IFFT block really necessary? Instead of using the IFFT block, is it possible to just place the original set of complex numbers (vectors) on the queue....and then transmit those numbers (real and imaginary components) - one at a time - through a QAM block?

The signal (without using IFFT) is still going to be OFDM, right?

Thanks for any comments/advice!
The “O” in OFDM stands for orthogonal.  The IFFT takes a complex number (1 bin of the input) and turns it into samples of a sinusoid of a frequency that, over a certain length (of time), is orthogonal to (and thus, under ideal linear conditions, won’t interfere with) any other frequency subcarrier output by the IFFT.

If you just transmit the original bits, the impulse response of the channel can smear the bits together, interfering with the adjacent bits, and leave the decoder/demodulator the interesting job of unscrambling this mess.  Depending on the channel response and how it changes over time, this may or may not be more difficult to do.