It looks like you are using salami tactics. Salami tactics works in both ways.

You say that nobody will went crazy when a tactic nuke will be used against RF army. Right?

Can you draw the line, please? When this war between two nuclear states will be nuclear, if even use of tactical nuke is not enough for you?

Ukraine isn't a nuclear state. They destroyed their nukes and joined the non-proliferation treaty in 1994.

Ukraine is a nuclear state[1] that temporarily doesn't have nukes - they gave all to Russia.

[1]Budapest Memorandum was not fulfilled, so Ukraine regain their status of nuclear state.

I’m just saying that the US isn’t going to engage in a massive species-ending strike over the Russians using a tactical nuke in a conflict with a non-NATO country.

No idea what salami tactics means.

The idea is that a tactical nuke requires at a minimum proportionate response. The history of large attacks is that the response is always disproportionate. A German plane accidentally drops their bombs on London leads to a dedicated air raid on berlin leads to the blitz.

A tactical nuke used against Kharkiv would certainly lead to either a Ukrainian dirty bomb strike against Moscow and or a NATO intervention. Why would Russia stop at one nuke when fighting NATO? For each tactical nuke against NATO you would expect at least one in return, or worse a megaton +x% for megaton exchange.

This spirals into full nuclear war very quickly once one side believes that they are going to lose without strategic weapons, or one side believes they have been or will be the victim of a strategic attack.

Speaking of, how long until the country with all of the old Soviet weapons facilities decides to re-enter the nuclear club?

Even total nuclear war (probably) wouldn't end the species. Just civilization as we know it.

That opinion is contrary to over 70 years of geopolitical and military strategic thinking.

I’m no expert, but my understanding is that thinking was based around a tactical nuke being used on US or Russian forces, leading to escalation and eventual use of strategic weapons, not against a non-nuclear power like Ukraine.

AFAICT, the person you were responding to wasn’t talking about a nuke being used against NATO forces.

If nuclear weapons are used it is doomsday. There are no qualifiers. The idea of getting away with a "tactical" nuke is fantasy. Our response would be total and immediate. There's no time to hesitate or wait for the effects.

If "tactical" nukes are a thing why hasn't anyone used them since 1945? Seems like they could have been handy in Syria or Afghanistan. There's no shortage of examples of nuclear powers going to war with non-nuclear non-NATO countries in the last 77 years. None of them involved nukes in any capacity.