Its not reactionary if you can enunciate what you want. As long as it is grounded in ideology, reasoning etc.

Reactionary leftism can not articulate why they want smth other than "its anti-right wing".

And both right and left are not singular entities, there are lots of different group each with different characteristics.

Take example of American right wing, there is a growing sub group that is becoming anti israel. Reactoionary leftists then start moving towards israel, using israeli talking points to attack other leftists because "it doesn't feel right" or "that's a right wing position".

Whereas, if you are grounded in your ideology, you would take advantage of the situation to further your own agenda like anti-imperialism or anti-capitalism or pointing out contradictions and furthering class-consciousness.

But when your guiding philosophy is "not right wing" you miss all of that.