Sometimes, I think, you can only judge that something is reckless by outcome, like it or not. It is perfectly possible to perform a stand up, chest to chest / choke tackle without incident, without anyone raising an eyelid, and in fact if it becomes a turnover maul the player praised and rewarded for it. But one or two dynamic changes - possibly outside the tacklers control - suddenly that well rewarded and praised action becomes a red card. What's the difference?
Are they both 'reckless'? Arguably in the big picture, maybe reckless is the wrong word, there is certainly risk (to you and oppo) in an upright tackle, and also reward. I think the important bit to consider is that the player has chosen to make that type of tackle, if he / she had chosen to bend at the waist and tackle that way then the risks are different, and that's the end result the game wants, different choices.