?? You using logic wrong. The comparable is taking those off CTA and enigma. Conviction isn't part of warlocks kit.
If there was a single build in the game that used any of those for auras then sure. But there's not except niche garb stuff like summon nec and bowazon. Being able to create an end game power character for 1 or 20 hard points in a skill is silly.
My problem with the choice is the lack of consistency, not whether it actually stays or goes.
If you can't have it because its expensive then the same sentiment should at least be considered to apply to paladins, sorcs, barbarians and others who had their good skills pushed into items and spread around. Teleport is a Jah and Ber, Battle Orders is a Mal Ist and Ohm, paladin auras and their respective costs etc.
If you can't have it because its too strong, balance other parts of the kit that rely on the Conviction and leave the option, and if it is too strong then start whacking the other s tier builds that trivialize the game in the same manner. Meanwhile hammerdins are even stronger than they were and nobody seems to have the same problem with them.
Give me variety. Taking away options is a lazy way to balance things, and pushes builds into cookie cutters where the only personal touches end up being trivial like the graphic and layout of the charms in your inventory. I agree that one point shouldn't create an end game power character. But with synergy requirements and an 80 point investment? Would 40-45+ in the skill allowing Conviction to still happen be that bad? Would it break it or add an option?