As I am reading BIP 141, there is a sentence saying "Wallets should always be wary of anyone-can-spend scripts and treat them with suspicion."

Does this mean that by default anyone-can-spend scripts are disabled and cannot be used?

Since segwit is a soft fork, what would happen if a miner treats some of the segwit outputs as anyone-can-spend scripts (as pre-seg scripts) and spend them in a new block?