Lords of Order Clerics and Paladins Optional Rule

I certainly agree that the Lords of Order have an Alignment that's best described as 'LH' - Lawful Harmonium. What's important to them is Lawful behaviour and commitment to the cause. Most 'evil' people in the Harmonium are so because of the methods they use rather than their actual ideology (Saeduenical herself is a good example of this), and to the Gods (as with many members of Orthorian society) this is less important than your commitment to the cause. So, I'm definitely with you on the issue of acceptable cleric alignment.

However... as to messing with the spells, no.

1) First and foremost, we're now straying into the alignment rules. Long years of experience have taught me that there are as many views and DM-specific systems for Alignment as there are actual players of the game. Most people however will either stick to the book-system, make a minor tweak as suits their style or campaign, or homebrew their own rules with much more detail and personal taste than we could do for them. Therefore I think we're best sticking with the core rules - because anyone who wants to really roll their sleaves up and get into the nitty gritty of alignment will do their own work anyway*

2) Alignment in D&D is objective, not subjective. Its a basic and fundamental premise of the game. If you don't like that and want to you use your own system that's fine, but see point 1.

3) This is the Prime Material Plane, and although I don't want to disrupt Ortho's flavour just to stick with the rest of the multiverse, there should be a compelling in-game reason why it works this way on Ortho and not anywhere else. Simply 'belief' and 'power of the gods' aren't acceptable reasons.

You're actually on the verge of opening a can of worms here: such as (just off the top of my head) does it only work on Ortho? On her colonies? What about Eallia, which isn't exactly fanatical about Harmony? Does it only affect spells cast by Harmonium members? Worshipers of a Lord of Order? What about worshippers of interloper deities? What about Harmonium worshippers of deities that aren't part of the 'Pantheon of Harmony'? What about non-divine versions of these spells and abilities? What about non-believers? What about chaotic individuals who do believe that basically the Harmonium/OCA is a good thing? And the biggie - if it works that way on Ortho, why doesn't it work that way in the Planes where belief is all the more powerful than on the prime.

4) Primers just aren't as concerned with alignment as their counterparts on the Outer Planes. The concept of philosphy and philosphical differences are probably confined to, well, philosphers on the prime. The average person is probably more concerned with "are you a good person (to me)?" which isn't exactly the same thing.

5) The Harmonium as a whole, much though it generally tries to be good, also isn't as interested in your Good/Evil axis as it is in your Harmonium membership and commitment. Now they might be very interested in your Chaos/Law axis - but Orthorian law specifically doesn't care about your intent and motivations, only that you broke the law. I just don't think its a big deal for most NPCs.

6) The whole "I killed him because he's evil and now I'm up for murder" scenario is just too nice to eliminate by messing with the spells.

7) Because being Evil isn't a crime. Actually, even being Chaotic isn't a crime either. Both have social stigma and prejudice attached (as does Good in some places), but all are equal in the eyes of the law.

8 ) Detect Evil and its counterparts are integral to the Paladin and Blackguard. Being in the Harmonium doesn't change your commitment to Good (/evil), just your methods. Paladins should remain paragons of virtue and smiters of evil. Blackguards... well, blackguards are probably marginalised socially because they're champions of evil - and who want's to be friends with that guy? There's no rule in the Harmonium that says you can't advance however - although pledging your soul to someone other than the Lords of Order would be seriously frowned upon (and pledging it to a Demon Prince or Devil Lord is almost certainly against the law of exemplar worship).

*...although a sidebar on subjective alignment is a different matter entirely.

I always interpreted the "deific alignment shroud" in Eberron as being meant to deter players from whipping out Detect Evils and then investigating whoever doesn't pass the test, not to make society "work".

I think the mechanical change involved can actually be spun either way, as an aid to PC believability or to overall moral ambiguity. Being, at it's core, a purely mechanical change it's subject to interpretation. So, it may be wisest to bring it up as an optional rule and allow a DM to make that spin in presentation, while providing our insight and reason for why it may be of use and apply within society.

Exactly.

Stay with Core, but slap a big 'optional' sign on anything that's likely to be open to major interpretation by individual groups, and let each DM decide for themselves (that's why I haven't gone into real detail and new rules about firearms and solarium on the equipment list, for example).