I think many in the comments are reacting from negative experiences with redpillers, and rightfully so. But your point is valid in a vacuum: there's nothing wrong with kindling a friendship with someone you turned down for sex. That is - and this is an important point - they clearly understand that sex is off the table from hereon out. Or at the very least, you will be the one to initiate, thus giving them the green, consenting signal.

As we progress towards normalizing sexuality, we must also normalize rejection. That means, as discussed above, understanding boundaries for friendships. And thus in turn, those friendships with respected boundaries will become normalized.

But I should also emphasize that no one is entitled to friendships just because they were rejected from sex. I don't think you implied that OP, but I do think some are reacting to that idea nontheless - often because we face that toxic idea in modernity.