There are 99 houses in 50 state legislatures. Any leftist amendment would require only 13 of these legislative bodies from 99 to defeat ratification. In other words, three quarters of the state legislatures must ratify or 38 states. If 13 legislatures fail to ratify the amendment is defeated. Since ratification by legislatures requires both houses to consent, only 13/99 are required. That is very close to 13%.
After the last election Republicans control 69 houses of the 99 state legislative houses. Republicans control 31 of the 50 state legislatures. To stop any unwise or imprudent amendment would require only 13 of these 69 Statehouse is (from different states) or about 19%, fewer than one in five.
The problem will not be to stop left-wing amendments but to pass prudent conservative amendments which restore the Constitution by invoking the Constitution.
If the Congress of the United States elects to have the ratification procedures conducted by conventions rather than legislatures, the method of selecting the delegates to those conventions would be chosen by the legislatures. If only 13 legislative bodies out of 99 object to the method chosen by the other body because it is considered to favor a leftist amendment, there is no ratification forthcoming from that state.
By either procedure the odds of a liberal amendment getting past so many conservative legislative bodies in so many states is both arithmetically and practically remote.
Finally, this is only the last line of defense, there are innumerable steps along the way which make a "runaway convention" virtually impossible and render the need for the states to fail to ratify very likely superfluous.
There are 99 houses in 50 state legislatures. Any leftist amendment would require only 13 of these legislative bodies from 99 to defeat ratification. How many legislative bodies would it take to defeat a conservative amendment?
After the last election Republicans control 69 houses of the 99 state legislative houses.
So leftists have control of (99-69) = 30 houses, or (50-31) = 19 legislatures. They need only 13 houses to block the ratification? If so, they have them already.
Therefore, here is one more item for your fine list. Perhaps it's a variant of (1):
5. The ratification will be blocked by the leftists, as the bar for unanimity is very high, and there are enough Democratic houses to do this.
But note that this is not to oppose the idea; others have pointed out that massive popular support for changes may make it a political suicide to go against ratification. This is just to keep the math in order.