Both think ~

'Seem to be' says it all. Congratulations! There's a glimmer of hope that you haven't bought that they actually are progressive in attitudes. That term alone is as abused as 'atheist' and 'Christian' and about every other identity label these days.

What people call themselves often has little to do with what they demonstrate themselves to be, in the main. Atheists by and large pride themselves in having abandoned deities and theologies promoting them whilst having only turned to some other kind of secular, yet faithful, identity. Theologies are, in case you don't recall, very authoritarian. In the absence of one kind of 'authority', the tendency of our kind is to find another kind as a replacement; if for no other reason than to sport an identity that is larger, greater and smarter than the rejected one.

Most self proclaimed 'Progressives' are really just subscribers to political or other ideological cults that reject our established political system, similar to how atheists reject established theologies and ethereal gods. Self identifying progressives resemble atheists in terms of shared rebellious attitudes. Unfortunately, neither prevalent group has anything original to express without their new adopted orthodoxy's talking points (scriptures). They don't think enough of themselves to stand and reason alone.

Actual atheists who've abandoned theological cults by reason of reason alone need no greater authority for security; no group with which to identify for validity. Genuine independence and freedom of thought make adherence to group doctrines quite impossible. If guided by native reasoning, people will find themselves in the company of many groups at various times, depending on an issue at hand. The best part is though you might agree with a group position, it will usually be for reasons differing slightly or entirely from theirs. Mere presence among them will cause most to consider you 'one of them'; that is, until next issue, next occasion, when they are puzzled and even angered by your agreement with their opposition, also for different reasons.

Reason is the key. Is your reasoning native or adopted? A free thinking person is guided by the internal compass of personal evaluation in need of NOBODY ELSE'S ACCREDITATION. Free thinking is definitely progressive and liberal too; but in original meanings of the terms, not modern bastardized ones.
Confirmation or certification by 'experts' or groups isn't required because groups are anything BUT progressive or liberal. They are typically regressive and mediocre.

It reminds me of something humorous from an ancient country song from when I was a kid that drew a similar individual vs. group distinction. "I'm not an alcoholic. I'm a drunk. Us drunks don't have to go to them meetin's."

Many conservative groups are religious

I don't think so... If there was, this corona virus would be over and done with already.... but isn't that comment like saying "There is an over abundance of cats with fur?"

Ya gotta problem wit dat or sumpthin'?

Over abundance-- To have an abundance of something is to have more than you need. So how many progresives would you recommend the Atheists mix to have?

Athiests and Progressives have some things in common:

1. they can think
2. they do think
3. they don't tolerate bullshit

"Over abundance"....who died & appointed you arbiter?

I'm agnostic, but I'm progressive because I'm for the clear-eyed working people not blinded by propaganda.
Religionists are forced to be Republicans because they're anti-abortion, anti-gay, anti-science, anti-21st Century in general.

The ability to think and reason. This is not complicated.