The issue here is that a tense is formed by a change in the root.
To explain, think of the verb 'to drink'. For English to have tenses, the conjugation would be something like:
I drink = Present Tense
I DRINKUM = Present Progressive
I drank = Past Tense
I DRANKUM = Past Progressive
I DRUNK = Present Perfect
I DRUNKUM = Present Perfect Progressive
I DRONK = Past Perfect
I DRONKUM = Past Perfect Progressive
and Future Tense might be:
I DRENK
I DRENKI = Future Progressive
NO AUXILIARY VERBS.
In English, this is only the case with the Present and Past Tenses.
For convenience, however, it is far simpler to refer to the different forms as 'tenses'; and it is the rare exception who is outraged at the idea of saying we have a 'Future Tense'.
If there is PRESENT TENSE and PAST TENSE there must necessarily be FUTURE TENSE.
You would think that wouldn't you, but contrary to what many grammar books tell you, it's not the case. Tense is a system marked by verb inflection or auxiliaries. There is no verb in English that is inflected for future tense, and the 'perfect' which is marked by the auxiliary "have" is a past tense.
What makes you think that English does not have a FUTURE TENSE? Any reference to futurity is termed as FUTURE TENSE
English does have several ways of talking about future time, the most basic one involves the auxiliary "will". But "will" is an auxiliary of mood, not tense, so it cannot be a tense marker.