Fact: Vedas contain worship of one and only one Paramatma
Logics given by believers of this myth are as follows:
Logic 1: Vedas contain names of many Gods and Goddesses
Refutation: (a). Paramatma is omnipotent and limited human mind cannot comprehend all attributes of Paramatma at same time. So vedas contain prayers to same one Paramatma. Different mantras however focus on different attributes of Paramatma and hence use different adjectives for Paramatma.
(b). Even Vedas claim that there is only one Ishwar and not more than that.
Logic 2: Vedic suktas have names of Devatas associated with them. These are the various Gods and Goddesses.
Refutation: The name of Devata associated with Vedic mantras refer to the subject of that particular sukta. That has nothing to do with various Gods and Goddesses in conventional sense. There are 33 devatas referred in Vedic texts, but this is also clearly elucidated that these refer to inanimate objects and not worth being worshipped. Vedas clearly proclaim that Paramatma is One and He alone is to be worshipped.
The whole confusion comes because ignorants assume Devata to be synonym of Paramatma. Devata means something or someone that gives, enlighten or illuminates. So in many contexts, Paramatma is also Devata. But so is soul/ Atman and all other animate and inanimate objects which satisfies this meaning of Devata. Thus parents, teacher, scholars, spouse are also devatas. Devatas deserve respect because they give us selfless benefits.
But Devata is not the goal of Worship, only Paramatma is, and Vedas are extremely clear on this.