Remember when you had to build Magic Resist or else the enemy support would kill you

You've never played against bitch bane sona have you

Clearly you haven't run into an Annie, Brand, Zyra, or Vel'koz support before.

It depends on what champions you are talking about. For tank & fighter supports flat MR glyphs are a must. For enchanter & lane bully supports it isn't really a requirement. If you sit melee as a range champion vs any tank support you are going to die. These are the basic pages:

• Tank support: Health regen quints, Armor marks, Health seals, MR glyphs
• Enchanter support: 2x AP quints, 1x CDR quint, Armor marks, Health seals, CDR glyphs
• AP bully support: 3x AP quints, Mpen marks, Health seals, AP glyphs

With adc been stronger now you will see a lot of supports go AD marks:

• Tank support: Armor quints, AD marks, Health seals, MR glyphs
• Enchanter support: 2x Armor quints, 1x CDR quint, AD marks, Health seals, CDR glyphs
• AP bully support: 3x AR quints, AD marks, Health seals, AP glyphs

Actually, Tahm Kench will probably kill you even if you build MR. The intended counterplay is "Don't let him get to you", and Riot acknowledged there were some champs that couldn't do that when they should be able to do that. They are looking into it. Maybe he will be nerfed in a patch or two. Maybe not. You trust me on my word, or I should find a link?

and that's a good thing, except that tahm kench's problem is doing damage while being unkillable

I guess you've never played against a Brand, Zyra, or Vel'koz support before.

Pepperidge Farm remembers.

You were saying?

You've never played against an AP Support or a "Support" then, I assume?