I think there is a distinction. Bitcoin proponents who are enthusiastic about SC believe BTC the currency is inseparable from the value in Bitcoin the blockchain and don't see the threat.

Where many Proponents pushing for protocol changes actually see them as separate and have devised a mechanism (SC) to do it.
 
The community enthusiasm for SC is evidence people overestimate the resilience of Bitcoin.

I forgot to add that miners if for profit only ones without Bitcoin savings should welcome MM SC as they get a better return on there mining investment and would be handicapped if Bitcoin diminishing block rewards were limited to Bitcoin the dominant Value Chain.

Looking at examples of past pool operators one may even be incentivized and financially motivated to lock value in the side chain with an attack on Bitcoin.

Thanks for reading cypher these ideas are not mine but to be distilled built on or disproved.