The arguments against Cruz are deceptive at best. The Birther Movement and the Trumpsters are misreading SCOTUS opinions that have nothing to do with Presidential eligibility and cherry pick comments in opinions that are part of the rationale portion of opinions and are not part of the decision. Some are doing it out of ignorance, but many are doing it to fool people.
The law (U.S.C 8, Section 1401) supports Cruz and that law has yet to challenged in court. You do know that most Constitutional challenges start with the relevant laws and in the end a successful challenge overturns the law on grounds of a Constitutional test. That has yet to happen, so all of these “experts” are just wind bags. This process is not a popularity contest among the various references out there in Internet Land.
It is difficult to reply without making assumptions about how you (or the argument you are referring to) uses 8 U.S.C. § 1401 to support eligibility for Cruz, so please correct any of the points below that may be incorrect. The argument you are citing / suggesting / making would be something like this:
1. Cruz (and his mother) fall within the conditions in 8 U.S.C. § 1401(g).
2. Given that Cruz (and his mother) fall within the conditions in 8 U.S.C. § 1401(g), 8 U.S.C. § 1401 provides that Cruz is a "citizen[] of the United States at birth".
3. A "citizen of the United States at birth" is a "natural born citizen" under Article II.
4. Therefore, Cruz is a "natural born citizen" under Article II.