"HOW Do You Know That Is True?"

It's HOW you think, rather than what you think that really matters.   Every claim needs to be supported by evidence, not dogma.  Unless such is the case, a claim should not be accepted. 

Yes, there are the religious, proponents of alternatives to medicine and other adherents to various pseudosciences whose beliefs are not based on science but on non-evidenced ideology.  However, there are also many people who are atheists, and/or are against some alternatives to medicine or some other pseudo sciences who arrived at such beliefs through other than skepticism/critical thinking, or science-based thinking. No matter the actual beliefs, if one arrives at their beliefs through other than skepticism/critical thinking or science-based thinking, one is open to accepting a non-evidenced belief. 

Non-evidenced beliefs ARE the problem in society today.  Imagine if all politicians were science-based thinkers and only acted on evidence instead of dogma.

If you are an educator, and/or are just interested in the topic of critical thinking, I recommend this link:

Critical Thinking Educational Materials