If they hijack the chances of a good treaty, the only alternative will be war.
you have an error in your premise....well...more than one.
You are assuming the treaty is a good one...a treaty is a good one ONLY if both sides adhere to it. Exactly what gives you reason to believe Iran will adhere to it? Their past? Their open desire to destroy a sovereign nation? The fact that they fund terrorism? The fact that they moved quickly to meet the first deadline?
Secondly.....stricter sanctions...whats wrong with that?
I know..."sanctions don't work"...I get it.....but...."Iran adhering to a treaty will? Really?