Are ANY two cards mathematically playable with huge pot odds?

[Poker Clif]

I recently had a situation where I called a raise with A6s preflop, early in a micro NLHE MTT. Sounds pretty bad, except that I only had to call $20 into a $480 pot.

It turned out rather well, as the flop was A66. But it got me thinking--with those odds, are there ANY two cards that aren't playable?

If no, does the following logic apply?

1. You should stay in a big pot with weaker odds than those that would keep you in a small pot.

2. With pot odds that are big enough, it is mathematically correct to call whether the pot is small or large.

3. Therefore, if you are last to act and everyone else at your table shoves on the first hand of an MTT, you should shove also. You have good pot odds and the pot is large.